Minification is the process of removing unnecessary data from files without affecting the functionality of the file.
Compressing is the process of reducing the size of a file (like a zip file).
Both these methods are ultimately used to reduce the size of files, which means there’s less for the user to download, and the website loads faster.
Most cache plugins will come with the option to minify & compress your CSS & JS files, so refer to the list of plugins there.
Divi also has the option for this in the theme options, but make sure you only have this set in one place or it can cause issues.
We like to turn it off on Divi and do it with WP Rocket instead.