The Steem blockchain requires a set of people to create blocks and uses a consensus mechanism called delegated proof of stake, or DPOS. The community elects 'witnesses' to act as the network's block producers and governance body. There are 20 full-time witnesses, producing a block every 63-second round. A 21st position is shared by the backup witnesses, who are scheduled proportionally to the amount of stake-weighted community approval they have. Witnesses are compensated with Steem Power for each block they create. So in other Words
Witnesses make sure there are blocks produced on the chain. They ( we as @blockbrothers )

• runs an active & up-to-date node, as a bare minimum requirement;
• engages actively with the community;
• is skilled technically;
• understands the Steem Blockchain on multiple layers of interest;
• adds value to the Steem Blockchain & Ecosystem.
  That way we all can benefit from the steemit blockchain. To make sure it stays that way everybody get 30 votes , and we are a witness and thats why we educate people about this.
  But if its to much for now a proxy can be set you dont gave to vote, we do it for ya.
  Britt