money is debt

Steem print new SBD the way they don't dilute the STEEM supply. STEEM is backed by the market, it has value because the market participants think it has value. SBD is different, because if we let the market decide its price, it would fluctuate as any other unstable currency.
So, Steem print an SBD "out of air" and says that anyone who has 1SBD will get 1USD worth of STEEM for it at any time. So the Steem network releases a debt note that must be payed back in the future with STEEM.

what my voting power

I'm using Busy at most of the times, so I don't need to go elsewhere to check that. You could also see your voting power there, but there are many different sites that provide that information.

What is a weight

The voting weight is the percentage that you can set while you are upvoting or downvoting contents. That means you don't use all of your power for a given vote when you set a percentage less than 100%. For e.g. if you would be a whale, and find a good picture you want to upvote, but your vote with 100% weight would give the author $1000 for that, you can set it lower to give your upvote without irrational rewards.

how do I view fellow steemians activity

SteemStats is a good place when you want to view other users activity.