To avoid confusion, I'm putting very brief definitions on the following terms. Some spoilers.

Angelic Layer is a game where two or more people compete with their dolls. It's a game of skills; it takes a lot of concentration to make dolls do complicated acrobatic moves. It's invented by a man named Mihara Ichirou. Originally, he created dolls as a model for making prosthetic devices for physically-challenged people, but the idea was rejected by companies which provided the finances. However, Suzuhara Shuuko inspired him to make a game after it. After four years or so of research, the game was introduced to the public and it became a big hit.

Dolls (or Angels) can be bought in toy stores (called Piffle Princess, I think). They come in egg-shaped containers and are 'hatched' in a tub of water. The people who buy them are the ones responsible for designing (e.g.: clothes, hairstyle, whatever) and giving them personalities (ie: agility, strength, whatever). They don't move by themselves; they can only move on a specific surface called the Layer.

Deuses are the people who control the dolls. They have to wear special head gears to make their Angels move. There's no particular age to become one; as long as a person has the dedication and the talent, s/he can participate in the game.