If you are not familiar with extra variables, refer to Ansible - --extra-vars (variables) command line option.

Extra variables can be defined a various places in Tower, such as in a Job Template, in Inventory, or in a Credentials Store.

From the Templates view:

1. In the left panel of Ansible Tower, select Templates.
2. Select the green plus icon.
3. Select Job Template.

From a Project:

1. In the left panel of Ansible Tower, select Project.
2. Select the Project that you want to associate with the Job Template.
3. Select the Job Templates button.
4. Select the green plus icon.
5. Select Job Template.

In this example, two extra variables have been defined, using the YAML format. This would be the equivelant of using the --extra-vars command line option.