Trainees boss sent first to the base (8)
I believe the answer is:
students
'trainees' is the definition.
'boss sent first to the base' is the wordplay.
'boss' becomes 'stud' (both can mean a metal decoration).
'sent first' becomes 's' (est letter of 'sent').
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the base' becomes 'ent' (I can't explain this - if you can you should give a lot more credence to this answer).
's' put after 'ent' is 'ents'.
'stud'+'ents'='STUDENTS'
Can you help me to learn more?
(Other definitions for students that I've seen before include "Learners or scholars" , "Sent dust to those who learn" , "Pupils at school, university etc" , "Pupils, learners" , "Learners as at school" .)