Garage band. Open App, select an Audio track, press the record button and off you go.
For field recordings, or any quick recording of Ambient sounds, conversations and general messing around, Acoustic ideas etc; It does the job for me with minimal fuss.
Also it's easy to go into the timeline and cut the Audio up into smaller Audio events, along with tidy up/get rid of anything I don't need. And of course I can add FX if needed.
If I have been depping on any shows, It has been perfect for recording in the pit for my notes and getting a general feel for the show while going over/reading through the charts at home.
It's pretty easy really.
https://support.apple.com/kb/PH24832?viewlocale=en_US&locale=en_US