1. Create a Nabble forum
2. Within the forum go to: Options > Embedding code
3. Insert the snippet of code you find there into the code behind the page on your site where you want it to appear.
Exactly how you do step three depends on how you built your site.
I have a lot more help for new forum owners on my GregHelp site.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.