While opening a file which you were editing earlier, you might see the message prompting that auto-save data is available, and whether you wish to recover it. If you wish to do that,

Press Enter

Now you will be prompted for filename. Enter it.
Confirm that you wish to recover autosave data.
You may sometimes be asked:

...htdocs/user/config.php locked by [email protected] (pid 18467): (s, q, p, ?)?

You have the following options:
sSteal the lock. Whoever was already changing the file loses the lock, and you gain the lock.
pProceed. Go ahead and edit the file despite its being locked by someone else.
qQuit. This causes an error (file-locked), and the buffer contents remain unchanged–the modification you were trying to make does not actually take place.