Joining blue party, fellow secures seat (7,2)

'joining blue party fellow secures seat' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'joining blue party fellow secures seat' is the wordplay.
'joining' indicates putting letters inside (inserted letters join the word).
'blue party fellow' becomes 'saddleup' (I can't explain this - if you can you should give a lot more credence to this answer).
'seat' indicates one should take the final letters (I've seen 'seats' mean this).
The last letter of 'secures' is 's'.
'saddleup' going around 's' is 'SADDLES UP'.

Can you help me to learn more?