with walking, start with 3 frames

(referencing cookie’s image above):
first frame, pose your guy like the 1st “contact” image

second frame, pose your guy like the 3rd “passing” image

third frame, pose your guy like the 5th “contact” image

with tweening on, that’s almost all you need
but then you can build up on
you can go and add a frame between frames 1 and 2 and use the forward/back onion skin as a guide

same with a new frame between 2 and 3