The Device.CLI.Modify Config activity allows you to modify the configuration of device or a selection of devices.
CatTools will Login to each selected device in turn, execute the configuration changes you describe, and will log any failures to the report file:
Whereas the Device.CLI.Send commands activity does this from the normal command line prompt (or Enable mode if that option is checked) this activity executes commands in the Config mode (Config terminal).
Note: A simple way to test this activity and get more used to it yourself is to do a change of interface description, using the commands in the example below:
description this is a test
Try copying it and using a different description, so you can run them in sequence and flip the description back and forth.
Maybe combine it with a Device.Backup.Running Config, so you can see the changes in the config files, the email reports it generates, and so on.
For more information see Setting up the activity