Spaces are an important tool to categorize your documents and to set the access rights for your users.
Via the box icon in the upper right cornenr you'll get the overview about your spaces. You could add as many spaces you want and you are ably to change or destroy them if you want to.
Filter your documents after spaces
Every document sits in a space. You are able to filter your documents on the start page by spaces or you could show all documents of all spaces.
Copy or move your documents to another space
Surely you could move or copy your documents to another place. Just click the space badge on the document to open the move/copy-window.
Set access rights
You could allow or block specifc places for every user. For example: The sales team could only see documents of the space "Sales" and the CEO could see every document.