The lore videos probably are your best bet unless you want to get obsessive. Even though I hate the format of 'dude on screen explaining something that could be written down and read in 1/10 of the time' .... ........
.........
.............
The actual lore is spread across so many of the rule books and actual novels that you would probably have a few years of reading to do. A summary from someone else about summaries and random headcanons on forums of the lore is going to get you there a lot faster.
Bloody soviets never win either.