You can save your sidebrain data into a file, and load it again in a later session.
If you want to keep data from session to session, put a call to
(sidebrain-load-from-file)
in your .emacs, and
(sidebrain-save-to-file)
somewhere where it will be called as you exit emacs.
You can also run these commands interactively.
Alternatively, you can set the variable
sidebrain-save-after-commands to something other than nil, and
each sidebrain operation will save the file automatically.
To customize the save further, see Customizing the save.