Solver questions

So I have been playing for several years mostly a slightly winning player. I have done minimal solver work but right now I don't have access to a solver. Instead I purchased post flop+ an app on the phone that puts you in different spots at different stack depth and then you choose bet sizes and actions and it really made me realize how terrible I am at poker in this solver age. My ELO is - 111. When I get a hand wrong I can click on the action and it will show me a range split of what the solver would do. Not having a solver I keep finding myself in spots where I am trying to do what I learned from earlier mistakes only to find the solvers action contradicting what I thought I learned last time. My question is can any one recommend videos online where I can get a better understanding of how and why solver does what it does?

I was also wondering how something like this was even created. The millions of EV calculations for every possible spot in poker just bends my mind. I feel like most of my a ha moments would come being able to see how a solver plays versus itself. To see it take a line and see how the other side would play it. Anyway any help or recommendations would be greatly appreciated.