Does concussion cause damage to brain?

Yes. In the mildest cases there is temporary damage that causes loss of consciousness. There may not be detectable damage, but there is always damage to the brain. Damage for multiple concussions is cummulative.
Yes. Sure does. Whether permanant or not is still being studied. That is from a single event. The damage may be obvious, such as altered thinking, headaches or subtle such as decreased memory or poor learning skills. One should see a specialisdt.