Upset, cross and losing the head with guide - that's what you have to go through to get into The House! (7)
I believe the answer is:
doorway
'guide that's what you have to go through to get into the house' is the definition.
I can't tell whether this defines the answer.
'upset cross and losing the head' is the wordplay.
'upset' is a reversal indicator.
'cross' becomes 'rood' (rood is a kind of cross).
'and' means one lot of letters go next to another.
'losing the head' becomes 'way' (I can't explain this - if you can you should believe this answer much more).
'rood' written backwards gives 'door'.
'door'+'way'='DOORWAY'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for doorway that I've seen before include "Threshold, portal" , "Room access, threshold" , "Entrance to a room" , "Opening" .)