What Happens to My Files When I Erase My Hard Drive for a New OS?

I'm not very tech-savvy, especially with my HP running Windows 11, so I have a question about switching to Linux Mint. I use Obsidian for my documents which are saved in markdown format—these files are incredibly important to me since they contain all my university work.

I read in the Mint installation guide that if I choose to 'Erase disk and install Linux Mint,' all data on the hard drive can be lost. Does this mean my personal files and pictures will be deleted too, or is it just the Windows system files? If I need to back these files up before proceeding, can I use services like Google Drive, or do I need to stick to a USB drive? Thanks for any help!