Hi Sumiso,
I read about it on the internet.
Actually, there's a local fellow who had done some non-holster leatherwork and gave me some tips, but ultimately I ordered my materials from Tandy (tandyleatherfactory.com) and followed some step-by-steps that I found online after looking at LOTS of high-end holsters.
I find the hardest part to be figuring out what the cut pattern should be, and in what order things should go together if they're complicated.
1/8" craft foam is cheap and works as a very nice stand-in for making holster patterns without the anxiety of cutting up your nice clean leather. Then you trace the outline of the pattern onto the leather and cut it out. From there it's just drawing your stitching lines, punching the holes, and then lacing it up in front of the TV. Molding, trimming, and finishing is a snap, assuming you've put your stitching in the right place.
I'm certainly not the expert on this stuff around here, but I was very enthusiastic when I started and took a bunch of pictures and documented the process somewhat.
My inspiration was here:
http://unblinkingeye.com/Guns/Holsters/BH01/bh01.html
And my learning thread is here:
http://www.rugerforum.net/showthread.php?t=8415
It's really really satisfying. If you have hard-to-fill requirements (or not-marketed-to requirements... or you're a cheapo like me) or unusual guns that people don't make stock holsters for, it's a great way to go. If you're marginally crafty it's not difficult. After the first couple holsters you'll have made your money in materials and tools back (if you don't go hog wild on tools!). Tandy often has regular sales on their holster-weight veggie-tanned leather.
I'd be interested to hear from rcmodel in what order he does his decorative patterning, dyeing, and stitching.
-Daizee