dota has a few aspects that do not make it as friendly to beginners (theoreticly), the main two differences that i know of is that in LOL you have a free teleport back to the base (opposed to dota2, which requires you spend gold on tp scrolls if you want to tp back to base or any of your towers.). As well as in Dota2 there is the ability to deny creeps, which is to at the last moment kill your own creeps which prevents the other team from getting experience from the creeps death, however if you are being match made with other beginners you won't have to face that as much.
both have some of the worst members (and sportsmanly like conduct) of any online multiplayer game that is out there. you will experience people who will quit the match and throw the entire game, for the pettiest and most inane reasons, more often than you will not.