Starting a freelance online business?

For the past year I've been taking publication cles so that I can do freelance work such as creating flyer's, brochures, calendars, etc. I found several websites that I can advertise with. I would just have the information sent to me like for example if someone wanted a flyer for advertisement of an event I could create it and send it back to them via email or burn it to a CD ready for printing, at a very low cost. Is this illegal or something? Is this even allowed? Let me know thanks!