I've made this wallet a couple times now. I use a laser cutter because it is a lot faster (albeit stinkier), but this pattern could easily be done with scissors, a rotary cutter, or exacto knife for the outside, and a leather punch for the inside. There are some great tutorials already on Instructables for dyeing and saddle stitching--neither of which I am particularly good at, so it is probably best to look at someone else's work if you're interested in that part specifically. Pattern is up as an .ai, pdf, and png.
When I make this as a gift, I like to engrave or stamp some kind of meaningful symbol into the wallet--urinary tract for a urologist friend, periodic table for a chemist, etc.
All of these can be easily found on Tandy Leather or Amazon or perhaps your local arts & crafts store.
Step 1: Cut the Wallet
Either print pattern and use it to trace the shape or download the ai/pdf to laser cut the leather.
If you're laser cutting, try taping down the leather to the print if it isn't lying flat. It will curl up when you cut it, and that's okay as long as it lies flat-ish before/during the cut. Warning for laser cutters: leather smells terrible when it is cut--a bit like burning flesh. However, after you dye and process the leather or even just wait a week or two, the smell dissipates.
Step 2: Dye the Leather & Wet Press Leather
Dye and wet press the leather.
Dyeing tutorial here: https://www.instructables.com/id/how-to-dye-leather/
Dyeing tips: Use actual leather dye. I tried using navy blue Rit fabric dye once because I could find my leather dye and it did not work well. The leather turned out a sad barely tinted purple-ish. I've used watered down acrylic paint before which will work to color your leather (and cover up that burnt flesh smell if you laser cut your leather), but that also isn't ideal. Furthermore, if you live somewhere very cold like me, leather dye does not do well if it goes through a freeze-thaw cycle, so it might not be the best idea to order it online in the winter during sub-zero temperatures if you aren't going to be home for a few hours.
Wet press: To wet press, after your leather is dyed, get your leather wet, then press it into your desired shape. I put some towels and books on top and left it overnight. I have tried to speed up the process by baking the leather in my convection oven before on a low temperature and it definitely dried the leather quickly, but I must have had the temperature too high because it left the leather with some burn marks and looking more vintage than I would prefer in this instance.
Step 3: Saddle Stitch Your Leather
Saddle stitching is something that I still struggle with, so don't take your saddle stitching advice from me. The only real advice I can give if that if you are punching the holes yourself, don't make them too big and wait for your leather to dry before stitching it because wet leather warps easily. Seriously. Whenever I try to take short cuts, terrible things happen.
Saddle stitch tutorial: https://www.instructables.com/id/How-to-saddle-stitch-leather/