Save information
Most applications save as you go, so there's no save button. For example, Memos keeps what you type without being asked.
On a screen with a Done or Save button, tap it to keep your changes.
If you're not sure, check that your change is still there before you close the application.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.