Howdy, Rube. Good to see you getting started with leather working. There's not a lot that can be more rewarding than that.
There are a lot of simple borders you can do. Take a look at Tandy's border stamps. The live link isn't working so here's the direct link:
https://tandyleather.com/collections/tools/stamping-carving+stamps_border-stamps
This one was done with a swivel knife cut, beveled on the inside then stamped with a D436 (actually an old version of that but it's almost the same). After that I ran a beader around the outside of the cut line. Ignore the basketweave on the inside and you have a nice looking border. You can vary that with almost any border stamp or textured bevel stamp. I also ran the beader along the edge of the leather where a sltitch line would go on a holster.
If you want a little more texture inside the border, you can make evenly spaced swivel knife cuts (any spacing) in two directions, diagonally or straight across. On this one, I also used a border stamp on the outside of the beader as well.
One more example. On this one, I stamped with a small veiner outside the beader.
OK, one more. this one is actually a copy (sort of, using modern stamps) of a border design from the 1800's. It's two swivel knife cuts, beveled and beaded, border stamps outside that (the very outside one is a small veiner) with a wide veiner stamped across itself in between. Just about any stamp along between the lines will do fine.
The possibilities are endless. Practice a little on scraps until you have the pattern you like. I make coaster sets to try out ideas. Some look good, some I toss before anyone can see them.
I look forward to seeing what you come up with.