I am guessing you are trying to use one of the 8x switchports that exist on this Router?

These are Layer 2 ports only, i.e they can be Access Ports in a single Vlan or a Dot1Q trunk to a downstream switch supporting multiple Vlans.

IP addresses can only be configured on a Layer 3 port.

Your only real option to use these ports is to create a Layer 3 SVI for each Vlan/subnet you want and then use the L2 ports as designed.

So effectively, if you wanted to create Vlan 50 with an IP address of 192.168.50.1/24, you would do:

!
vlan database
vlan 50 name xxxx
exit
!

This would create the Vlan

Then

!
interface vlan 50
description xxxx
ip address 192.168.50.1 255.255.255.0
no shut
!

This would create your virtual Layer 3 port (SVI) and you would then need to provision your Layer 2 ports to support it.

If you have a switch that is going to be connecting to the router, you will probably need to configure the Router port as a dot1q trunk as below:

!
interface gi1
switchport trunk encapsulation dot1q
switchport mode trunk
description Downlink to Switch
!

Obviously you switch needs Vlan 50 creating and a Trunk ports towards the router.

If you are just plugging in hosts (PCs/Laptops/Printers) directly to the Router, you can create an access port for each host in Vlan 50.

!
interface gi1
switchport mode access
switchport access vlan 50
description Printer
!

You can create more than just vlan 50, this is just a single example.

Hope this helps!