Definition of muck about:
(v) :
(informal, intransitive) To do random unplanned work or spend time idly
(v) :
(informal, intransitive, British, Australia) To be playful; full of fun and high spirits; to treat a situation unseriously.
(v) :
(informal, intransitive) To attempt to do something with a piece of equipment without understanding how it works.
(v) :
(transitive) To play with; to toy with; to waste the time of (a person).