start off by installing the clients
then ask your friends to teach you, if they r busy,
then this is the actual guide, u pick any hero and stick with it until u r bored of it, u buy anything that u think is useful, after doing that, most likely the pros will either call u nub or ask u why did that buy that certain item and etc.
that way u know what to buy and what not to for ur hero, also sticking to 1 hero for a long time is gd because u can see other human playerred heroes in action, u can see how they use it and what do they buy
from there on, u can stop using ur default hero and start using other heroes,buy items for ur new hero and therefore the items that u buy will probably be what u saw when other peeps used the hero WHEN you were using your default hero.
this is what i did, so i m kind of messed up but i can survive the *cough*mean community there