Thanks, Noodle, and great it's opening some new doors to peer into.

Witnesses are the people who keep the Steem blockchain going. They process blocks, keep the price feed updated, and so on. Many of them run projects for Steem users or develop applications users can use for certain purposes. Voting for witnesses allows them to keep their witness nodes (the servers used to witness blocks) going, by allowing them to process more blocks the higher in the witness ranks they climb (with thanks to votes). It can be likened to a direct democracy in a way.

Have a look at the link for the list of witnesses in the top 50 ranks:
https://steemit.com/~witnesses

You can also look through the #witness and #witness-category tags for witness updates about what they do for Steem and their projects. And you're welcome to come ask in the witness channel on the Block, and the witnesses who support the Block, and the Block them, can answer your questions if they're available, if other members aren't able to.

Gmuxx has a great post about witnesses you may find helpful:
https://steemit.com/witness-category/@gmuxx/what-are-witnesses-what-they-do-and-why-you-need-to-support-them