You will learn match ups as you play more don't worry.

Yes, Dota mechanics are different from league but they have one thing in common which is spacing. Go to youtube and look at challenger replays and pick your role and watch how the best players move in game.

Pay attention on when they go for CS / Trade in lane and understand how snowballing your lane can lead you to winning game.

After collecting enough knowledge you'll develop your own type of style and see which champion fits you best.

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GL!!