They will interview you, and check your hormones, do an ultrasound, once you are deemd ok to donate you will begin the meds.
The medication protocols can vary, but the basics are:
You take a medication to stop your cycle, might be injections, might be birth control pills.
Then you take a medications, a daily injection (very small needle in your tummy or thigh) to grow eggs. You will have to be monitored by vaginal ultrasound to watch them grow. Once the eggs (egg follicles actually I guess) are a certain size they will extract the eggs.
You will be sedated during the procedure. I recommend you find out what type of sedation and if you will be completely out. The extraction is very painful if you are awake. If I did it again I would ask for Diprovan, which can only be given by an anesthesiologists I think.
Then you are done.
The medications can have side effects, and carry some risks. Most people are fine, but you should look it all over to make sure you are comfortable with the risks.