Will come after, you understand (6)
I believe the answer is:
follow
'understand' is the definition.
(I know that follow is a type of understand)
'will come after you' is the wordplay.
I cannot really see how this works, but
'will' could be 'll' (contracted form, as in 'he'll' - 'he will') and 'll' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for follow that I've seen before include "'____ and don't dilly-dally on the way'" , "Ensue" , "dog" , "Succeed; go after" , "Come next" .)