Usually, all ports are created equal...that is, port labels are printed for ease of use, not because some ports can only be used for incoming or outgoing traffic. So, choose some of the copper or SFP ports for your WAN(s).
That said, there are of course exceptions to that rule.
The "s1" and "s2" ports are dedicated sniffer ports. I haven't used them for that yet but I guess there is some info on "one-armed sniffer" in the Handbook.
The "vw1" and "vw2" ports form a "virtual wire" pair. Traffc is flowing in one one port and out the other (Layer 2). Again, please look it up in the Handbook.
The "mgmt" port is pre-configured for local-in management traffic. In the config, you'll see "set dedicated-to-management enable". Given that, you can assign an IP address from a subnet that is already in use on a different port. And, the "mgmt" port does not participate in routing.
