Fortigate explicit Proxy and proxy policy

Hello All,

Iam trying to understand how fortigate explicit proxy works and how is the traffic flow with explicit proxy and proxy policies.

How do a traffic flow ( Client to Fortigate firewall as a proxy -> Proxy Policy -> normal policies -> ) , or is they any other way this works.

Do we need normal policies for explicit proxy or we don't required.

Any documents or related content i helpful