Sunscreens protect from sunburns by blocking and diffusing UVB. Only few brands protect from UVA as well.
Sunscreens are meant to protect the skin from UV. They do prevent sunburns effectively; it is not clear if they are as effective against cancer and aging. Sunscreens have SPF (Sun Protection Factor) between 5 and 50. Besides the SPF, sunscreens have different base. Some are water-proof, meaning you can sweat and swim without bothering about the exposure; some have aloe, or cocoa butter, or tea-tree oil in them. Some are marketed for children, others for great looks, and yet others for hikers and surfers. I'm an unfortunate redhead who needs sun protection in Michigan in April. I need plenty of SPF and I don't like cosmetic smells and the texture of cream. Children products are for some reason just not as good as real things. Beauty products seem overpriced; at least I don't know what make them cost their weight in gold. But people who go on high altitudes have very real chances to get sunburns. I searched for my sun protection in the outdoors supplies store. They recommend to brands: Bullfrog and Sower. Sower is a traditional thick white cream. Bullfrog is a clear gel based on alcohol. It dries quickly, forming a water-proof film, it's not sticky, it has no smell besides alcohol which evaporates. Bullfrog comes in SPF 15 to 45. It costs about $10 for 5-ounce bottle. I use it on my children, as well.
SPF applies only to short-wave UVB which causes sunburns. Longer-wave UVA is not reflected by zinc or titanium oxide and not effectively diffused by regular organic component of suscreens. UVA is the part that goes deeper into skin and can cause cancer. Some brands claim both UVA and UVB protection.