Keep is a lightweight note-taking application, designed for when you just need to quickly jot something down that you can throw away later.
Think about sticky notes - those little squares of coloured paper that you write on as a little reminder and bin once you're done with it. If it's something you might normally jot down on one of those, then that's what Keep is for. Keep can be used for lists (you can even tick off the bits you've done), notes or reminders.
Due to the 'throwaway' nature of Keep, it does not utilise a version history. It does, however, have options to Undo and Redo.
They can, but you must be mindful that there is no way to share a note that only gives viewing permissions. Any user you share a note with will be able to edit or delete that note.
There are several ways to organise your notes. You could give your notes different colours depending on their category, you can 'Pin' notes so they always appear at the top, or you can give notes labels that are searchable. Labels will appear in the menu on the left-hand-side and clicking a label will show only notes that have been given it.