We cannot see these light rays because ultraviolet rays are invisible. The only way to detect or see an ultraviolet rays is by using a certain satellite, however some satellites only detect a small portion of ultraviolet rays. An example of a satellite capable of detecting ultraviolet rays (or radiation) is NASA's "International Ultraviolet Explorer" which has been used for over 17 years now.
A good way to lower the chance of getting skin cancer from a UVA or UVB sun ray is by putting on a suntan lotion that says "broad-spectrum". Broad-Spectrum means that it will block both UVA and UVB rays, as others might partially block either one of them. The most important one to avoid is the UVA ray because it is 20 times more abundant then UVB rays and the skin damage can last longer or even be permanent. UVB rays aren't as bad as UVA rays because they only come around during the summer and the worst it can possibly do to you is a dark sunburn.
The rays are not called A and B because they are alike. The A in UVA stands for the word "aging" because it goes into your skin and causes wrinkling. The B in UVB stands for the word "burning" since it is known to cause skin cancer from serious sunburns. UVB rays are stronger when they are near the equator. It's possible to get infected from a UVA ray even when your indoors because it penetrates clouds and glass. It's a good idea to put on sunscreen on a sunny day if your indoors because of that.