I had a student a few years ago who was really struggling with the multiple choice portion of all of my exams. She had learned to write a decent essay, though she always stuggled a little to include enough detail. The multiple choice portion tripped her up every time, though.
Around March, her grades started improving dramatically. I asked her what she was doing differently.
She said "oh, you know those primary source readings you always assign to us? I started doing them, and it made it much easier to understand the multiple choice questions." (The multiple choice questions on AP History exams are often based on primary source readings.)
<headslap>
Trust your teachers.
Most of us have been doing this for a long time.
The difference between a 4 and a 5 (or a 3 and a 4) on the AP Exam is a kid who does the readings consistently throughout the year.
Especially this year, when we're all struggling to cover the content we would normally cover in class (I estimate that I'm MAYBE able to hit 75% of my normal content), we rely even more on students doing the readings outside of class.
In a normal year, I'd spend 2-3 days talking about why Europe developed absolute monarchy and Louis the XIV. Then I'd spend another day discussing Peter the Great, and maybe one more day comparing Louis XIV to Peter the Great. This day I did Absolutism in 2 days. Total.
Yes, there are videos like Crash Course to help students understand information. When I was working to outline a syllbaus for the Crash Course European History series, my job was to look at the course description and decide what should go in each episode. There is NO WAY that we covered 100% of the information, and everything in the syllabus did not make it into the scripts. Your textbook covers everything, though. Videos are a great supplement, but they are not a replacement for your textbook. They do not help you practice analyzing primary sources. They simply do not have the level of detail that your textbook does.
So learn the lesson now that my former student did not learn until March:
READ YOUR BOOK. For real.