Is very straight forward from a linux machine and a little bit different on a windows machine.
First step is to download the .iso either the NVIDIA version if you have a nvidia card pick that one otherwise use the non-nvidia version.
As you can see quite straightforward.
The second step is to create install media either on a cd or more likely a usb you have laying around.
The way to create install media from the downloaded file varies from system to system but here are a comprehensive set of instructions.
Is to actually install Pop-OS on your machine. Follow the steps at the following link
Install Pop!_OS On Your System76 Computer - System76 Support