Grab on to the thing and don't move! (4,2)
I believe the answer is:
hold it
'grab on to' is the definition.
I can't judge whether this definition defines the answer.
'thing and don't move' is the wordplay.
'thing' becomes 'it'.
'and' says to put letters next to each other.
'don't move' becomes 'hold' (I can't explain this - if you can you should believe this answer much more).
'it' put after 'hold' is 'HOLD IT!'.
'the' is the link.
Can you help me to learn more?
(Other definitions for hold it that I've seen before include "Stop right there!" , "Cease action - get a grip!" , "Hang on a minute" , "Informally, cease action" , "Wait" .)