Russian verbs aspects
There is a brief discussion of verb aspect in the LinQ grammar guide for Russian. You can find it by clicking on your profile icon in the upper-right corner of any page when your selected language is Russian. The discussion of aspects is near the bottom.
There is a course specifically about verb aspect at https://www.lingq.com/en/learn/ru/web/library/course/35391
There are three lessons in that course. Maybe they will help.
Hopefully others can offer some more resources.