Start betting with something that’s easy to understand (4,4)
I believe the answer is:
open book
'something that's easy to understand' is the definition.
I can't tell whether this definition defines the answer.
'start betting' is the wordplay.
'start' becomes 'open' (opening is a kind of starting).
'betting' becomes 'book' (I can't justify this - if you can you should believe this answer much more).
'open'+'book'='OPEN BOOK'
'with' is the link.
Can you help me to learn more?
(Other definitions for open book that I've seen before include "Something that can be easily interpreted" , "Face etc that can be easily read" , "Person easily understood" .)