To use a diaphragm, follow these steps: 1. Apply a teaspoon of spermicide inside the dome and around the rim. 2. Fold the diaphragm in half with the dome pointing downward. 3. Insert it into the vagina, aiming towards the back. 4. Ensure it covers the cervix completely. 5. Leave it in place for at least 6 hours after intercourse but no more than 24 hours.