To your question about email messages: They will not be deleted, unless you choose to delete them. The best place to save email messages is within your email software. The same software can do searches. You can classify your email into folders for improved organization.
About learning how to use Windows 10:
Years ago I got fed up with all the disasters I was causing on my computer. Trust me, you don't know what a disaster is ... I do. I decided to bite the bullet and finally learn how to use my computer.
I started off with a novice-level book on Windows. I mean, computers for Richard and Jane. (You can't say **** in this forum.) I worked through every chapter and did all the exercises. Then I moved up to a slightly more advanced book, going through every chapter and working all the exercises, and so on. Over time I gathered more ability and more confidence.
You don't have to use a book; there are other media. But the idea is the same: Start at the bottom and work your way up. It's tempting to short-circuit the process - don't do it.
However you learn, make sure you're getting well-qualified, professional instruction. It takes a while to discern good quality advice from junk.
All the time and effort you spend on this will bring great rewards. You will become a competent, confident computer user. Then, maybe you can come back here and start answering questions. 😉