they give you anesthetic, so youll be asleep for the procedure, then they dilate your cervix, and use a tool that has a vacuum on it to suck everything out. Theres risks, but there low and mostly associated with the anesthetic.
If you are worried about the risks associated with anesthetic, as I was, you can request an epidural. I was given a light sedative that helped me sleep, and an epidural for my D&C as I had an intense fear of anesthetic after birthing Noah.