Not sure where you're from, but since I am currently going through the same process I thought I would chime in.
In Illinois, to become a salesperson you have to pass a 45 hour course and a state exam, then find a broker who will sponsor you. I took the class online (realestateexpress.com) and it was very straightforward. It was great preparation for the state exam which I took last week.
After passing the exam, you may seek a broker to sponsor you and/or continue on to earn your broker's license, which requires an additional 75 hours of coursework. I did this online as well, and I actually finished the 75 hours of class in about 10 hours over a span of 3 days (I used realestateexpress.com again). I am now scheduled to take the broker's exam tomorrow, only 1 week after passing the salesperson exam. To me, this was well worth doing because the broker's license allows you to practice independently if you choose and because it will soon be mandatory to be a broker in Illinois (salesperson licenses are being eliminated, leaving only brokers and managing brokers). This will also improve your credibility overall education.
So, in a nutshell all you need to do is take a class, pass the class, then pass the state exam. At that point, you have 1 year to find a sponsoring broker or sponsor yourself if you did the broker class. As far as choosing an office to go work for, they all vary so you will want to interview various firms in your area to see how they split commissions, pay office expenses, and handle floor time and incoming leads. You will want to find out any other requirements they have and how they can help you as an agent grow and succeed.