In addition to encrypting your entire device you can also encrypt only files that you select. The files are then inaccessible unless you unlock them using set password. You can use these files as you would any other file, and then lock them again when you’re done. The advantage of file-specific encryption is that it offers an extra layer of protection in case someone gets hold of your computer when it’s not turned off (and therefore the full disk isn’t encrypted)
To encrypt specific files you can use VeraCrypt. See this tutorial for instructions.