The basic shape is usually copper, at least for beginners. The glass that is bonded to the copper shape is a special ground glass called frit. The coefficient of the glass and copper must be as close as possible so the glass will not pop off the copper base.
After selecting the copper form and your colors, the first step is to pickle and wash the copper form. Pickling solution is an acidic liquid used to clean the enameled piece between layers of frit. It must be treated with respect, and gloves and safety glasses used when working with it. An apron to protect your clothes is also a good idea. The pickling solution must be kept warm to prevent thermal shock when the hot piece is placed in it. Each time the piece comes out of the pickling solution, while you are still wearing your gloves, you must wash the piece thoroughly to remove any of the pickling solution. Then you are ready to add the next layer of frit.
As each layer of frit is added, the piece is run into an enameling oven, which is similar to a kiln, but it has an opening that allows you to put your piece and take it out as needed. You can also watch the glass frit melt into the previous layers. When the current layer is melted, remove the piece and drop it in the warm pickling solution.
If you are planning many layers of glass on the copper, You will have to enamel the back to help relieve the stresses between the glass and the copper.
If you are really interested in learning to make enamel jewelry, find a glass studio that has enameling classes, or an enamel artist who will give you instruction. Once you learn how to enamel jewelery, you may find that enamel jewelry is the hobby you have been looking for.