Overwhelmed by test, sorted out lesson (8)
I believe the answer is:
tutorial
'lesson' is the definition.
(I've seen this before)
'overwhelmed by test sorted out' is the wordplay.
'overwhelmed by' means one lot of letters goes inside another.
'test' becomes 'trial' ('trial' can be a synonym of 'test').
'sorted' indicates an anagram.
'out' is an anagram of 'uto'.
'trial' placed around 'uto' is 'TUTORIAL'.
(Other definitions for tutorial that I've seen before include "Rail tout (anag)" , "Personal teaching session" , "Session of intensive teaching to an individual or small group" , "Seminar" , "Class" .)