To configure interface port in CLI
1. Assign name to an interface
(config)#interface name <interface ID> <interface name>
example: (config)#interface name "port1" "outside"

2. Configure port speed:
(config)#interface speed <interface ID> <Speed>
example: (config)#interface speed port1 auto

3. Configure Maximum Transmission Unit (MTU) by default its set to 1500 bytes
(config)#interface mtu <interface ID> <MTU size>
example: (config)#interface mtu port2 1500

To configure interface port In webui array OS 6.4 or later: (in mode "config")
Under "system configuration" -> Basic Networking -> "Interface" tab -> Port (Interface settings)