Industry Structure

Gaining work as an illustrator can be difficult, but there are a few ways to break in. The most stable way you can earn money by illustrating is to work for something called a Design House, this is a company that employs illustrators, you would be paid in a salary rather than working for commission, though you would lose all rights to your work, and you wouldn't get personal recognition, you would become just another worker for a design house, most illustrators who used to work in a design house are very relieved to no longer work in one, it seems very constraining for illustrators.
Another way to work as an illustrator, would be freelance, pretty self explanatory, you work by commission, people come to you asking for work, you quote them for the work, then you get paid for that work, and you can reserve copyright, or you could sell that as well so that they now own that work entirely, this is probably the most common way illustrators work.
You can also work as a commercial illustrator, designing logos or advertisements. You could work as an on board illustrator for a magazine or other in print companies.