Webhook looks like you are talking about JIRA integration with salesforce.
Yes. I worked on this...
There are two part for this integration
You need to create a rest service on salesforce end
Also You need to create a site so that webservice will be available without login to org..
Once your rest service and your site is ready...
So Now if I want to access that rest service then I need to use url like
https://site-name-here.force.com/services/apexrest/your rest service end point here.
Next Jira webhook part....
You need to use above url in Webhook.. Add url and select events when post methods should called...
And just setup completed.. You will recevice all JSON data from JIRA to salesforce...