Agree, pretty simple. I just rescreened several windows where the cats felt they had to make a personal statement.
New screen material, the spline tool and the spline can be found at any Lowe's or Home Depot. Just take a little piece of the old spline along with you so you get the right size.
On ours, you have to push up
very firmly on the screen to compress the spring clips at the top (which are what keep the screen from falling out) in order to get the bottom
of the screen out of the slot it slides in. The fixed screens, which don't slide have little spring-loaded pins which must be pulled up to remove the screen- sometimes these get corroded and don't want to pull up. Squirt a little PB Blaster or other penetrating oil in them to encourge them.