Gnu Emacs is a text editor created in the 80s based on Gosling Emacs, which was created in the 70s. The first version of gnu emacs was ported to unix. And it became increasingly popular due to its configuration possibilities, since Gnu Emacs allows you to configure it in real time with a kind of terminal, and also with its own lisp dialect that allows you to configure it via its init file.
First you have to find your .emacs.d folder, this varies from operating system to operating system
on windows:
C:\Users\YourUser\AppData\Roaming\.emacs.d
on mac:
/Users/YourUser/.emacs.d
on linux:
/home/YourUser/.emacs.d