how do i create a NAT rule between a LAN interface and mobile or between a LAN interface and WiFi on a RUT955, have tried following the manual but was not able to find that information it, is it just from the firewall area? wondering if there are other ways to do it?
This depends on your requirements. General SNAT can be configured i Network → Firewall → NAT rules. There, you can create additional rules and specify what traffic should have the source IP NATed. For DNAT, you can configure port-forwarding in Network → Firewall → Port-forwarding. This will allow you to create rules that will match specific packets and redirect them to your desired host.
For more complicated rules, you can add your own IPTable rules. Those can be added in Network → Firewall → Custom Rules. If you are unfamiliar with IPTables, you can lookup for some information about it online. An online article here is decent.
General information about Firewall on RUT955 can be found here.
We also have a wiki article about Traffic Rules here. While this article is not specifically for NAT, it can be helpful to understand some of the basics.
thank you so much