To protect yourself from the sun this summer, remember to apply your sunblock or sunscreen at least 15 minutes before going outside. You also need to reapply every 3 hours, and more often if you are sweating or go in the water.
Clothing, hats, and sunglasses are in addition to sunscreen use. Look for a sunblock or sunscreen which is at least SPF 15, and SPF 30 is even better. If you have sensitive skin, you will do better with a sunblock (e.g. mainly titanium dioxide or zinc oxide) rather than a sunscreen.