Which SPF?

I try all kind of sunscreens, but I still manage to get a slight burn every time. I'm only 13 and I know it's good for me to be concerned about my skin. I don't want sking cancer. So, can anyone suggest an inexpensive sunscreen that works?

SPF numbers indicate how LONG the sunblock will last on your skin. NOT how strong they are... For example, if you go outside without sunblock, you'll get sunburn in 20 min. If you are wearing SPF 10 sunblock, it will delay the burn for 10 times longer. 20min x 10 =200 min. For SPF 50 sunblock, it will be 20min x 50 = 1000 min.

The best sunscreen out there is coppertone waterproof,it's the one that comes in the blue bottle. Keep applying it all day. Put it on about a half hour before you go out into the sun, or at least before you go into the water. you want it soaked into your skin before you get your skin wet or it will just sort of puddle on your skin and not work. Put it on again after you get out of the water, or if you don't go in the water, put it on every few hours, so you don't burn. Use an SPF of about of about 30 to make sure you don't burn. Sit in the shade every so often to cool off your skin.

You should start out by sitting in the sun for a short time at the beginning and build up until you have a base tan and then stay a little longer