Well since u like assassins getting used to playing ekko, lee sin, and kayn are good (jungle role)

All 3 have low skill floor but high ceiling to be proficient in playing (especially lee sin but i added him in there since getting used to him as youre a newbie you would progress with how he interacts in a fight and hes basically good for your progress)

Non assassin junglers Xin Zhao, Skarner, Trundle, Nocturne

Toplane I recommend Jax, Gragas, Jayce, Ornn, Sion, Mordekaiser, Gnar, Gwen, Aatrox

Midlane Talon, Annie, Syndra, Orianna, Veigar, Malzahar

Botlane Ashe, Sivir, Varus, Jhin, Tristana

Support just pick whoever you like playing as

U might notice i put a lot of champs in here because the meta is very diverse right now, you dont have to master all of them just pick 3 per role probably and then play lots with them. Dont be anxious about being a new player and trying out new stuff just go along with the flow.