For basic snapshot documentation, click here.
If the standard control panel doesn't give you enough control over your snapshots, you can always access them with FTP. Simply use FTP to access your site as usual, then look for the "snapshots" folder in the root of your account. Note that is the parent of the "pages" folder where the site files are stored. Snapshots are not publicly available, which is why they are not stored in the "pages" folder.
Snapshots stored in the "snapshots" folder will be available from the snapshot control panel. After a snapshot is created, you can download it using FTP, then delete it on the server to save that space on your account. If you ever need to restore that snapshot, simply upload it to the "snapshots" folder again, and it will be available from the snapshot control panel.
Snapshot files are standard .ZIP archives. Do not attempt to modify the contents of the archive since this may result in undesirable behavior.