Great Summery @dutch.

Your SP determines how much influence your votes have over the rewards pool. If you have more SP, your votes are worth more.

This is very important for newbies to understand. I would also like to add some points that I feel would be helpful for new steemians:

1- You can increase your Steem Power by earning payouts from your posts. The amount you will receive is determined by how much upvotes your post receives.

2- You can also increase your SP (and hence your influence) by buying Steem from exchanges and powering up.

3- You can delegate your steem power. Delegation is like renting. You still own the SP, but the receiver gets to use the influence they possess. @minnowbooster uses this idea in its services.