How to play Dota 2 for free? You can do it if someone (me in this case) sends you an invitation code.
You will need to download and install Steam and after that Dota2 via Steam.
I recently got about 13 DOTA2Beta gift code keys which I don't need, so if anyone needs one or two, just write in the comments bellow
The keys are entirely free. First comes, first serves.
PS: please no Russians. Unless you will play on the Moskow server or speak English on US/EU realms then it's fine.
Dota2 is a product by Valve, powered by Steam.