Autumn Leaves is a jazz "standard" that is played at almost every jazz gig/jam you go to!
As part of the AMEB CPM Bass Step 2 syllabus, students are asked to create a walking bass line for Autumn Leaves in the key of G Minor. In the case of working out what the key of a tune is you can either look for a key signature or at what the last chord of the piece is which in this case is G Minor.
The walking bass line below plays through the arpeggios of the chords for the first 8 bars. Then it gets more interesting as diatonic (meaning part of the scale of the key) and chromatic leading tones such as the E natural to F (bar 9) are added to create a more scalar bass line. In the video below the bass line is repeated twice to allow you to pickup on what is happening more easily.