Be careful where you download things, and know exactly what you’re downloading. Potentially Unwanted Programs (PUPs) are becoming common.
Installing a recently unsupported operating system so you can use an email program that hasn’t been supported for years is something I’ll advise against. There are safer ways to go.
Without the proper security others will be able to access your computer and your files, and even watch what you do online. Fortunately, setting up basic security is easy.
In order to figure out how to back up your email you first have to figure out where it lives. It might be on your computer; it might be out on the internet.
The answer to this is simple. If it’s only in one place… it’s not backed up!
The biggest key to learning is to follow your own curiosity. So don’t be afraid to poke around, read what you can, and ask questions.