IMO it's a good idea to get the harmonic material sorted at least a bit before you start to fool around. No idea about how much general scale/chord relationship knowledge exists round these parts, also no idea how much of it is covered in the videos posted above, so I'll try to keep it short-ish (uhm...).
General formula of 7th chords (which is what most jazz is kinda based on) building up on any major scale (using roman numbers for scale degrees is a common thing for that sort of stuff):
I maj7
II min7
III min7
IV maj7
V 7
VI min7
VII min7/b5
In C major (typical key for this to get explained - but fortunately "Autumn Leaves" isn't in C, so we need to deviate from that quickly, which is a good thing), the scale notes are C, D, E, F, G, A, B, so our chords are:
Cmaj7
Dmin7
Emin7
Fmaj7
G7
Amin7
Bmin7/b5
Now, "Autumn Leaves" (at least the Realbook version) is in Bb major or G minor (we will for a while ignore the "specialty" of G minor, namely the D7 dominant chord).
Scale notes of the Bb major scale are: Bb, C, D, Eb, F, G, A. Hence our 7 chords are:
Bbmaj7
Cmin7
Dmin7
Ebmaj7
F7
Gmin7
Amin7/b5
That's pretty much the basic harmonic stuff the tune is building up upon.
Next step would be to find some decent ways to play these chords - and I think there's at least one pretty easy method that I'd happily explain in case anyone's interested, but before doing so, I'd like to know whether everybody's more or less fine with the above or whether anything needs some more explanation.