Play ARAM and with time you’ll learn the characters. The matches are shorter and you can’t choose the champs, so you’re forced to learn. In ARAM you can only play with champs that you bought and have, or that are in rotation (set of characters that are free to play, changes every week). Because of rotation, you’re more than likely to see the same champs over and over so it makes learning easier. With time you’ll get the hang of it. Have item builds open on second monitor so you can focus on what abilities do instead of figuring out what items to buy.