How do I add a forum like this 'circle forum' on my website?

My client wants a forum on their site, specifically in the membership area. I tried to make a blog with comments work, but they want members to be able to start topics as well. 

If this function is clearly already on Squarespace, surely we have access to it, right?

@nicolehardesty Hi, did you manage to install a forum on the squarespace website of your client ?
One of my client is asking too.