The specifics for getting a real estate sales license varies by state. Generally speaking, it involves two things:

1. Education: Most (probably all) states require a certain level of education in order to get licensed. I'm not talking traditional college or vocational school. You'll need a certain number of specifc state and national real estate class hours, typically received at "real estate school". In Arizona, the requirement is 90 classroom hours. There are several real estate schools in the Phoenix area (and in almost every metropolitan area). Cost varies but expect to pay around $350.
2. Examination: You'll have to pass a licensing exam. Again the specifics vary by state. In Arizona the exam is two parts, state specific and general. The exam is not easy, but if you pay attention in your real estate classes, pass the school exams and study, you can pass the state exam. Cost (in AZ) is $90 to sit for the exam, and you need proof of completing the required educational courses.

In addition to education and examination, there are applications to complete (more fees...) and most states require a background/fingerprint check to be completed. Your real estate school and broker can assist with getting these done.

Getting your real estate license is only the first step. You'll need to find a broker, join your local, state and national real estate associations, and get MLSi access and a lockbox key (and yes, there are fees associated with all of this!). Many states, including Arizona, also require continuing education courses in order to renew your license.