Have a talk with your doctor. Make sure you understand why you're having it, what it involves, and any risks or benefits. If you have any questions or concerns, make sure to ask. Consider writing down your questions so you won't forget them. If English is not your main language, ask for an interpreter.
You may be asked to sign a consent form explaining the procedure. Signing it means you understand the risks and benefits, have had all your questions answered, and agree to have it done. If you have trouble reading, ask that the information be read to you. Or bring a friend to help you.