@Ftopacho Check Point for Beginners is a good starting point to learn how Check Point is working.
you have to configure new subnet/vlan/interface via GAiA WebUI
you have to add these new interface to the topology of the gateway in Smartconsole
you have to add these new subnet to the encryption domain
additional you have to configure routing, Antispoofing and some new rules for the needed communication
and at least you have to connect your new network physical via a new interface or via new VLAN on an existing trunk