If you have competed officially, you can click on "Export," sign in with your WCA account, and then press "Export to server (csTimer)." This stores your solves in the csTimer server, which keeps them safe in case you accidentally clear your cache. Alternatively, you can sign in with your Google account instead (if you have one).
You can also turn on "Auto Export (per 100 solves)" in "options" -> "global." Set it to whatever method you used to sign in.
If you want to import your session data (after accidentally clearing your cache or accidentally deleting an important session), sign in with your WCA or google account, and then press import. It will then overwrite your current session data if you press yes on the popup.