Begin to explain my activity at restaurant? (8)
I believe the answer is:
initiate
'begin' is the definition.
(thesaurus)
'explain my activity at restaurant?' is the wordplay.
I cannot quite see how this works, but
'at' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'to' is the link.
(Other definitions for initiate that I've seen before include "Cause (process) to begin" , "Cause to begin, launch" , "Start, begin" , "Cause to begin or admit to membership" , "found" .)