Perform successfully (7)
I believe the answer is:
achieve
'perform' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for achieve that I've seen before include "Consummate" , "Accomplish, gain by effort" , "Bring about, accomplish" , "Attain (goal)" , "Reach or accomplish" .)