Slips up about joiner’s assignments (7)

I believe the answer is:
errands
'assignments' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Perhaps there's a link between them I don't understand?
'slips up about joiner's' is the wordplay.
'slips up' becomes 'errs' (I've seen this in another clue).
'about' indicates putting letters inside.
'joiner' becomes 'and' ('and' joins words together).
'errs' enclosing 'and' is 'ERRANDS'.
Can you help me to learn more?
(Other definitions for errands that I've seen before include "Missions" , "Small jobs" , "Working trips" , "Short journeys" , "Trips to carry out tasks" .)
