The most basic automatic logging is to keep track of when a certain TODO item was marked as done. This can be achieved with40
(setq org-log-done 'time)
Then each time you turn an entry from a TODO (not-done) state into any
of the DONE states, a line ‘CLOSED: [timestamp]’ is inserted just
after the headline. If you turn the entry back into a TODO item
through further state cycling, that line is removed again. If you
turn the entry back to a non-TODO state (by pressing C-c C-t SPC for example), that line is also removed, unless you set
org-closed-keep-when-no-todo to non-nil. If you want to record a
note along with the timestamp, use41
(setq org-log-done 'note)
You are then prompted for a note, and that note is stored below the entry with a ‘Closing Note’ heading.