There are a few ways you can go here. A vinyl cutter, a printer/cutter, or
DTG.
A vinyl cutter is going to be your cheapest point of entry. This will allow you to quickly and easily create single color designs, lettering and numbering. Multi color designs can also be achieved as well by cutting and pressing each individual color.
A printer/cutter will allow you to print and cut full color transfer for nearly any type of fabric in any color regardles of how many colors. This system is perfect for full color custom and short to mid quantity runs. Some items you can do here are t-shirts, sweatshirts, shorts, pants, hats, gloves, bags, socks, decals, posters, banners, vehicle graphics, wall graphics, etc.
DTG or direct to garment printing, will allow you to print full color directly to shirts.