I hear you, Ed, have tin back up inside, joined (6)
I believe the answer is:
'joined' is the definition.
(I know that joined can be written as united)
'i hear you ed have tin back up inside' is the wordplay.
'i hear' becomes 'it' (I can't justify this - if you can you should believe this answer much more).
'back' indicates one should take the final letters (the letter at the back).
'up' is an anagram indicator (letters get chucked up).
'inside' means one lot of letters goes inside another.
The final letters of 'you ed have tin' are 'uden'.
'uden' is an anagram of 'uned'.
'it' going into 'uned' is 'UNITED'.
Can you help me to learn more?
(Other definitions for united that I've seen before include "Joined together as in alliance" , "... we stand, divided we fall" , "Of one mind" , "Agreed" , "in league" .)