Pull in this region nothing to smile about (5)
I believe the answer is:
groin
'pull in this region' is the definition.
'groin' can be an answer for 'region' (groin is a kind of region). I am not certain of the 'pull in this' bit.
'nothing to smile about' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'to smile' becomes 'grin' (grinning is a kind of smiling).
'about' means one lot of letters goes inside another.
'o' placed inside 'grin' is 'GROIN'.
Can you help me to learn more?
(Other definitions for groin that I've seen before include "Fold between belly and thigh" , "private parts" , "On rig (anag.)" .)