So you need to download GIMP? Let’s start at the beginning then!
GIMP is completely free to download and use. You do not need to pay any money if you don’t want to. Of course you can donate on the GIMP homepage, and I’d wager that the folks who create and maintain this software sure could use some financial support if you’d like to donate.
GIMP runs on many platforms, including Windows, Linux and Mac. The developers do a great job of including users from different operating systems and deliver an excellent product regardless of the operating system you choose (or not!) to use.
GIMP can be downloaded from the main site’s download page. Be sure to download the user manual while you are there as well so you can install it locally. It may come in helpful for you in a time of uncertainty and it won’t require an internet connection.