Before learning new heroes just go and learn about the abilities in demo and analyse them.
You can also test your skill by playing a BOT match.
Never pick new heroes(that you haven't played) in Matchmaking especially in Ranked.
You'll just ruin games for your team.


To Learn New Heroes --> https://howdoiplay.com/


here are some links to get you better at game.

Pos1 - Carry - https://www.youtube.com/watch?v=BKE72pDhLfc
Pos2 - Mid - https://www.youtube.com/watch?v=r7jVT_e9VMU
Pos3 - Offlaner - https://www.youtube.com/watch?v=BKE72pDhLfc
Pos4 - Soft Support - https://www.youtube.com/watch?v=k7CoR71Vapo
Pos5 - Hard Support - https://www.youtube.com/watch?v=wR7xkwavegk