The diaphragm is a rubber disc that is fit for size by your gyn and requires a prescription. It is placed in the vagina up to an hour before sex, with ample spermicidal jelly placed in the center and along the rim. It is left in for six hours after intercourse, and then removed, cleaned with soap and water, and placed back into its dry holder.
If a second act of intercourse occurs, a second applicator of spermicidal jelly should be placed in the vagina and the diaphragm is removed six hours after the last act of sex. With typical use it is 85% effective, and with perfect use it is 95% effective.
Use the diaphragm only with water soluble lubricants, and get a new diaphragm after 2-3 years of use, or if you have gained or lost 10 lbs or more. It may increase the risk of UTIs.