On the radio, breakfast item is expected at first to air in several parts (9)

'air in several parts' is the definition.
The definition suggests a verb in its base form which matches the answer.

'on the radio breakfast item is expected at first' is the wordplay.
'on' means one lot of letters go next to another.
'the radio breakfast item' becomes 'serial' (I can't explain this - if you can you should give a lot more credence to this answer).
'at first' says to take the initial letters.
The initial letter of 'expected' is 'e'.
'serial' put next to 'is' is 'serialis'.
'serialis'+'e'='SERIALISE'

'to' acts as a link.

Can you help me to learn more?