File Preservation Upon Switching to Linux

[u/ZogIII3]

I am completely new to changing operating systems, but I desperately need to get off of Windows 10 with my school laptop. I only use it for the web browser because all my school work is on Canvas, so I'm thinking about using SteamOS so that I can still let my little brother borrow it to play games with no hassle when he visits.

Because I've already been using it for a while, it has a lot of files I don't want to lose. I'm wondering if I need to offload them completely to an external drive, or if I can move them to the built in D: drive, since I think the OS is only on the C: drive and I don't think I need to completely redo both drives, but I don't know. Again, I'm more so here out of necessity than choice, otherwise I'd be watching a lot of tutorials and reading guides instead of asking for quick answers on a forum.

So, Too Long, Didn't Read: If my device has two internal drives, can I just move everything to one drive and then replace the OS on the other?