To configure emacs you can use the customize interface M-x customize, but I’ll often provide bits of code to put into your emacs config file. This is a file containing pieces of emacs lisp (the language emacs is written in) that alter the behaviour of emacs.

Your emacs config file is probably in one of three places:

1. in ~/.emacs though this is now a bit outdated and instead it will usually be in
2. ~/.emacs.d/init.el
3. but, if you are using my recommended set up prelude then your emacs config file will be in ~/.emacs.d/personal/. Any .el file in that directory will be read when emacs starts.

Once you make a change to your emacs config file, you can highlight the section of code and run M-x eval-region, or if it is a big change, you might need to restart emacs for it to take effect properly.