Login to your windows server and start Computer Management

Right click on Uses under Local Users and Groups and click on New User...

New User

Provide User name and password and name

This is going to be my kind of service account and I don't want to change password, that's why I have chosen Password never expires.

Click on Create.

Remember your user name and password, we are going to use it later.

Right click now on Group under Local Users and Groups

And Select New Group...

Provide Group name and click on Add...

Type User we just created and click on Check Names button

And then click on OK. And then Create button on New Group dialog.

In the real world you add Service account in your Active Directory or ask you IT Operations to create a service account for you. But the idea is more or less the same.