This guide is intended for players who have never before played Dota2. It only covers the basics of the game and nothing else.
1. Hero selection:
As soon as the game finished loading (and all the players) it is time to pick a hero.
Select one of the categories that are not marked red in the dropbox (look at the image below).
Just look for a hero that looks appealing and pick him. After the 1 minute timer has run out, press play (right below the image of your hero). For a small selection of starter heroes and explanation as to why those are better for beginners scroll to the last section of the guide.
2. Immediate start of the game.
It’s time to buy items. Click the icon on the bottom right where it says shop. It will look like in the next picture. Make sure to buy all the items under “Starting Items” (by right clicking every icon once). Do not buy boots first, it only makes sense in VERY special occasions.
In this case I also bought a courier. This little creature can be used to transport items from the so called fountain (starting point) to heroes. More info about the courier can be found at the end of the guide.
Now it’s time to get to the lane. There are 3 lanes usually called bot/mid/top-lane. There should be 2 heroes on bot, 2 on top and 1 in mid. The best would be to have 1 ranged + 1 melee hero on top and bot. For now just go to whatever lane does not have the mentioned amount of people yet and ignore the part about 1 ranged and 1 melee hero per lane.
3. Early laning phase:
Each hero is level 1 after the game started (who would have thought this….). To spend the skillpoint (every hero starts with 1) choose one of the spells to level up. Make sure to read what they do (hover the cursor above it) and preferrably pick one that says stun or damage. (That’s always good). The 4th spell can’t be leveled before a hero reaches level 6. In most cases it is a good idea to level the 4th spell when reaching level 6, as it is usually a really strong spell!
Also in most cases spells get way better the more points invested into them. So don’t evenly spread points but put them into 1 or 2 skills instead of all of them. After one of the skills is at its maximum of 4 levels, start getting another skill to level 4.
Left to the skills there is a small area showing the heroes stats (strength points, agility, etc.). Don’t spend skillpoints by clicking on that area until all the spells are greyed out (or in other words all the skills are maxed out).
Now it’s time to get gold and items.
Killing enemy heroes or creeps (those things running around in each lane) rewards gold. The thing is, they only reward gold to the person who actually kills it. This is called lasthitting and means that a creep should only be attacked when it’s life is so low that one attack kills it. So just wait until the creep has low health, then attack it to get gold.
Bam, loadsamoney. Make sure to not constantly auto-attack the enemy creeps. This will push the lane (being closer to the enemy tower is bad) and make last hitting harder. Of course enemy heroes will try to stop your team from getting gold. And your team should try to stop them from doing that. Make sure your hero is always above 50%-70% health when close to enemy heroes (better even more health). In case enemy heroes try to attack (and kill) your hero just run towards the closest friendly tower for now. Luckily (if you bought the starting items) there should be the following items in your inventory.
The first one heals a hero for 115 hp over time. To use it click it, then click a tree (yeah… you eat trees to heal yourself).
The second one heals a hero for 400 hp over time BUT if the effect will be lost upon taking damage.
The blue thing will regenerate mana. Just like the second item it will also lose its effect upon taking damage.
Those items are called consumables. The other items give boni to the stats.
4. Spending gold
Now if you have some money, spend it. You lose money if you die, so get rid of it. Make sure to buy all the suggested items for now and read their descriptions when you buy them.
Get those items in the order from top to bottom.
Some (expensive items) consist of different cheaper items. If you want to know what you need for one of those more expensive items, click it and you will see it in the bottom right.
Once you have all the small items in your inventory or your stash it will assemble itself into the “big” item. If you buy an item while not at the shop, it will be put into your stash. You can collect it by using the courier(more on that later) or going back to the fountain (the point where you start).
Some items can be bought from the side shops (almost every item needed for boots), some only from the secret shop, and some only at your fountain(where you start).
Blue = Secret shops, Yellow = side shops, white = fountain.
If you try to buy an item and you only can get it at the secret shop, the game will tell you so. No worries.
5. Push to win
Well, so how do you actually win the game…. by destroying the enemies ancient. If you take another look at the map above, there are buildings marked on that map. There aren’t many types of them. Towers, Barracks aaaand…. “buildings”.
Let’s start with towers. First off, if you kill one of them, everyone on your team will get 200 gold. Also if you get to be the one who throws in the “last hit” to destroy it you will get 500 gold extra. On the other hand, those things deal serious damage to you (and your creeps).
Be sure to use your creeps as meat shields while attacking them:
Also buildings in this game have backdoor protection. This means as long as the first tower was not destroyed, you can’t damage the second one etc.
Also if you attack any tower except the first one, it will regenerate health up to the point it was damage if there are no creeps around (and it regenerates fast!). So make sure there always are creeps around when you try to damage one.
After you destroyed 3 towers in a lane you can destroy the barracks. If you destroy those, the lane in which you destroyed them will spawn stronger creeps for you! They will also reward the enemy with less gold and always push the lane towards the enemy as your creeps are now stronger than theirs (taken that your barracks are still alive).
Destroying the ranged one will spawn stronger ranged creeps. Same goes for the melee barracks. If you only have time to destroy one, always go for the melee barracks. (one wave = 1 ranged + 4 melee creeps. Do the math 
)
Finally the ancient:
It is guarded by another 2 towers. Take those out, then take out the ancient to win the game!
There are also these things called “building”, taking them out will grant you a bit of extra gold but do nothing else:
6. Killing enemy heroes (or: this is actually the fun part):
Now this is where things get tricky as this is not something easy in this game. Basically the concept of clubbing someone to death is quite simple, but the problem is when there are others who want to do the same thing to you.
The basic rules for fight avoidance in your first games should be:
- Don’t take a fight under an enemy tower!
- Don’t take an uneven fight (2 vs 3)
- Don’t take a fight when you’re low on life (<50%-70%) or low on mana.
- Don’t run in first if you are not tanky (look at your team mates. If they have way more life than you stay back a bit).
Take a fight in the following situations:
- You are 3 heroes against 2 of them
- You are under (very close) to your tower.
- You aren’t close to their tower and an enemy is at/under 50% life.
Also try to kill the enemy heroes by surprise! Find someone else in your team willing to kill an enemy, then come at 2 (or 3) vs 1 to ensure an easy kill. The heroes with “stuns”, “slows” and raw damage spells (“nukes”) are the best suited for ganking (“gang killing”) since they can deal a lot of damage in a short period of time or disable enemies to make sure they can’t escape or fight back. Fights shouldn’t last too long. If you see they are surviving even after you blew up all your spells, it’s probably better to retreat instead of following them under their towers. (thx to Harfangdesneiges)