Even I started out pretty weak in those two bro. I did the entire video series first for theory only.
Then I did the DPPs given by my centre because I didn't know about PG books back then.
Also, in collisions, try getting more comfortable with oblique collisions which is very briefly explained in the videos bro. But oblique collisions must be done only after you are thorough with linear collisions( for any given value of e)