Welcome to the Ranch, Steven!
Probably the best place to start if you've never worked with the Pi is to download and install the Noobs image. It will allow you to select from a variety of OS choices.
The one that's probably best supported is Raspbian. It's a Debian Linux distro and it's what I use even though for desktops and servers I tend to prefer stuff from the Red Hat/Fedora family.
There are presently 3 versions of Raspian available from the Pi download site. The minimal one is very compact, but it does not include GUI. Unless you are a dedicated command-line geek, you'll probably want to skip that one. The other two are GUI versions and the only difference is in the amount of pre-installed apps that come with them. Everything's built from the same sources, so it really doesn't matter which one you choose.
Note that the Pi running the Raspbian OS is a full-scale computer, albeit one from about the year 2000 as far as performance goes. The new Pi 4 models are more powerful and generally considered fast enough that they could actually replace just about anyone's desktop. My own experience with that model is that the 1GB is cool, but if you start running a web browser plus a software
IDE that it will run short on RAM. The 8GB model on the other hand, is about as well-equipped as many laptops and at $75 a lot cheaper. You may find that the $35 1GB is sufficient for video games, though. Or maybe one of the in-between models.
For that matter, you can do a lot of gaming with the older Pi models. I used to play Minecraft on the Pi 3.