The steemd site will give you your voting power. I check that every day before I start using Steemit and check back over and over to make sure I do not drop too far below 80%. That will allow it to recover to 100% by the next day.

Reputation determines how your reply is listed in other people's posts. The higher the reputation, the higher your post will appear. Then the more upvotes it has, the higher it goes. People with low reputation will have their replies automatically hidden. They are often ignored or muted too.

Reputation is received most quickly by people with high reputation upvoting the replies of people with lower reputation. I was able to give you a couple reputation from a few 100% upvotes. Someone with 70+ rep could have raised you into the 50's though. Their vote is very powerful.

It makes sense too because people of high rep will typically know when a new person is going to deserve a high reputation or not. People can downvote (flag) you too, so there's a way to lower an account's reputation as well.