Trainee told to do things one at a time? (6)
I believe the answer is:
intern
'trainee' is the definition.
(intern can mean a trainee worker)
'at a time?' is the wordplay.
'at' becomes 'in' (synonymous in some cases - eg at school, in school).
'a time?' becomes 'tern' (I can't explain this - if you can you should believe this answer much more).
'in'+'tern'='INTERN'
'told to do things one' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for intern that I've seen before include "(American) hospital doctor" , "Confine - assistant medic in America" , "Confine the hospital doctor" , "Confine the hospital resident" , "22 [IMPRISON]" .)