u/Additional-Ad-766

I am learning concepts like NAT (Source NAT, Destination NAT, NAT Server), VPN(SSL,IPSec), security policies, nat policies and different profiles in firewalls like URL filtering profile or IPS profile. I am not following in what order incoming or outgoing packets are matched against different modules of firewall. I have searched the internet but I couldn't find consistent answer. Does anyone know good sources where I can read about this?