IFTTT is a bit of a hassle. It is an "if this then that" engine. You create an account using the email your Google Home is associated with, then search for Google Assistant. This should connect them.
From there, you need to connect your devices - such as lutron caseta. Best advice is to search the web for how to do this as there are tons of tutorials out there to help walk you through. Once you get the hang of it, it's not too hard, but can be time consuming if you have many devices to set up.