I haven’t started using webhooks yet, but to me it looks to be as simple as having a web server that needs a single route. During the subscription process Twitch will send a GET request to that, for subscription verify or subscription deny. When a subscription is active, and an event for that subscription happens, Twitch will send a POST request to that route containing the data. I’ve only had a brief glance at the docs though as webhooks are later on my todo list.
If you don’t want to, or can’t, have a web server running then poll the API as you would normally to get the data that webhooks would otherwise provide.