Just install the steam from store.steampowered.com/
click on the green button above , the try to install it.
try to update or you must create your own steam account ,
update until finished , then when steam account appears , look at the left bottom , and click add from code , enter your code and you have dota 2 at your library , try to download ( approximately 7 GB )
and update the dota 2 ,
hope this answer can help you and i prove it 100% TRUE , and dont forget mark my answer is the correct one / or best answer , if you want to play with me at dota 2 , replay your steam id , i will add you soon =)