Are you talking about making replacement/custom grips for your own guns, or doing it as a business? The techniques are pretty much the same but the way you approach the work is important. If you plan to go into business just making grips, you should take some business courses, and maybe (depending on what you want to do) get an FFL*, plus any and all the local licenses you may need.
The material is readily available, except for a few materials like genuine ivory; if you stick to wood, most kinds of wood can be found at local big box stores or specialty hobby shops. More exotic woods can be found by simply Googling on the net. A good source of walnut is old rifle stocks, which can be had for near nothing at many gun shops.
For skills, check the local community college. Quite a few have woodworking courses and while the world does not need more birdhouses, you can learn the basics, like how to use a band saw and retain all your fingers. You don't need many tools. You need a clean shop with ventilation, a good work bench, a rotating checkering vise (versa vise), checkering tools, inletting tools, etc. Get a Brownells catalog, and you will find most of what you need, includig grip screws and ferrules, though you might get better prices on some stuff from a wood-worker's supply house (Google again).
What you really need is practice, and lots of it.
Now the bad news. There are several companies turning out fully finished handgun grips in (what appears to me to be) every conceivable variety of shape, color and material. You need to be able to compete with them.
*You don't need an FFL to make grips. But if you install/fit grips on a gun for money, you are doing gun work, not grip work, and are considered a gunsmith, not a grip maker.
Jim