Series of lessons is nothing to swear about! (6)
I believe the answer is:
course
'series of lessons' is the definition.
(I've seen this before)
'nothing to swear about' is the wordplay.
I cannot really see how this works, but
'nothing' could be 'o' (looks like zero - 0) and 'o' is located in the answer.
'swear' could be 'curse' (synonyms) and 'curse' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for course that I've seen before include "Route along which something travels" , "Direction; lecture series" , "Route; studies" , "Layer (of bricks)" , "Flow" .)