It has a moving effect on a shifty varlet (6)
I believe the answer is:
travel
'it has a moving effect' is the definition.
The definition suggests a singular noun which matches the answer.
'shifty varlet' is the wordplay.
'shifty' indicates an anagram.
'varlet' with letters rearranged gives 'TRAVEL'.
'on a' is the link.
Can you help me to learn more?
(Other definitions for travel that I've seen before include "Go on a journey" , "treatment for a narrow mind?" , "Locomotion" , "Journey from one place to another" , "Go on a trip" .)