Ring John and Paul to begin with (4)
I believe the answer is:
loop
'ring' is the definition.
(a loop is a ring of material)
'john and paul to begin with' is the wordplay.
'john' becomes 'loo' (both can mean a toilet).
'and' means one lot of letters go next to another.
'to begin with' says to take the initial letters.
The initial letter of 'paul' is 'p'.
'loo'+'p'='LOOP'
(Other definitions for loop that I've seen before include "Noose" , "I cross myself" , "Oval or U-shaped coil or bend" , "Circular shape of pool" , "Endless film strip" .)