Since version 8.0, Ardour has had extensive support for the Novation Launchpad Pro Mk3, a relatively inexpensive grid/pad controller that unlike some similar has its own internal capabilities in addition to those provided by DAW interactions.
Plug the USB cable from the Launchpad Pro into a USB2 or USB3 port on your computer.
The Push 2 will be automatically recognized by your operating system, and will appear in any of the lists of possible MIDI ports in both Ardour and other similar software.
Normally, Ardour should be able to automatically detect a connected Push 2 device. If it fails, open the Preferences dialog, and then click on "Control Surfaces". Click on the "Enable" button in the line that says "Launchpad Pro" in order to activate Ardour's Launchpad Pro support.
Once you select the input and output port, Ardour will initialize the Launchpad Pro and it will be ready to use. You only need do this once: once these ports are connected and your session has been saved, the connections will be made automatically in this and other future sessions.