Light beams involve energy. Lasers are very very focussed beams of light. As humans there are only certain ranges of light that we can see, which is why there's such things as infra-red cameras etc.
To carry information, the light can be set to either fluctuate or switch on and off extremely quickly, in a way the human eye can't see, but a 'reader' at the other end can understand these fluctuations and turn it back into data.
Yes, lasers with enough intensity could cause damage.