It's obvious when an inexperienced driver is in distress (5)
I believe the answer is:
plain
'it's obvious' is the definition.
(similar in meaning)
'an inexperienced driver is in distress' is the wordplay.
'an inexperienced driver' becomes 'l' (a learner driver's car carries L-plates).
'is in' indicates putting letters inside.
'distress' becomes 'pain' (I've seen this before).
'l' going into 'pain' is 'PLAIN'.
'when' acts as a link.
(Other definitions for plain that I've seen before include "Flat land; unmarked" , "Geographical feature" , "open country" , "Unvarnished" , "Unflavoured" .)