Every item such as a document or to do can have its share settings individually set - e.g., to share that document with Mary, who is working with you on a particular project.
However, you can also set sharing at the folder or level. Whenever you set folder sharing, all documents in that folder (and any subsequently newly created documents) are automatically given the folder's share settings.
Before setting sharing, you might want to set up a share group for your friends.
To set folder-level sharing, choose an gray application tab such as "Document" and then click the small blue 'Share Folder' command under any green folder name:

You will then see a screen that lets you fill the share with controls with the names of the friends or groups you want to share the folder with.
Folder sharing works identically across all KeepandShare applications, including To Do, where it's called List Sharing.
Whenever an item or folder has sharing set, the 'sharing icon'
is displayed next to it. Hover your mouse over the sharing icon to see the share settings.
If you check the 'edit' box then your friends can create new documents and upload files into the folder. However, to guard against accidental deletion of important information, only you can delete the files and documents in the folder.