First we need to identify what the device's interface name is.
To find this, type the following at the command prompt.

pi@something:~$     ip  a

This will show you the various interfaces.
you should see something like , enp5s0:   

That is your physical Ethernet interface name.

To configure netplan, open the netplan configuration file.

Netplan Config file :

pi@something:~$   sudo nano /etc/netplan/00-install-config.yaml

Static Configuration : 

The blelow config is an example configuration of static ipv4 interface with the interface name being:  enp5s0

#====================================================================

network:

  version: 2

  renderer: networkd

  ethernets:

    enp5s0:

      addresses: [192.168.1.25/24]

      gateway4: 192.168.1.1

      nameservers:

        addresses: [ 8.8.8.8,8.8.4.4]

#====================================================================

DHCP Configuration :

Below is an example of dhcp configuration. 

#====================================================================

network:

  version: 2

  renderer: networkd

  ethernets:

    enp5s0:

      dhcp4:  true

      gateway4: 192.168.1.1      

      nameservers:

        addresses: [ 8.8.8.8,8.8.4.4]

#====================================================================

To apply netplan configuration, you can issue the following command :

pi@something:~$  sudo netplan apply

to test the new configuration before applying, please issue the following command :

pi@something:~$ sudo netplan --debug  apply