Where you'll find menu in message he carries? (4,4)
I believe the answer is:
home page
'where you'll find menu' is the definition.
The definition suggests a singular noun which matches the answer.
'in message he carries?' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'message he' becomes 'page' (I am not sure about this - if you are sure you should believe this answer much more).
'carries?' means one lot of letters go next to another (in a down clue, some letters go beneath others).
'home'+'page'='HOME PAGE'
Can you help me to learn more?
(Other definitions for home page that I've seen before include "First point of call on website" , "on-screen introduction" , "Introductory part to a website" , "introduction to site" , "website feature" .)