First go to "Add Ons & Integrations" on your dashboard.
Select Church Community Builder
Enter your church ID. The church ID is the first part of your CCB url. For example. if your url is yourchurch.ccbchurch.com then just enter "yourchurch".
Enter your API user name and password. If you don't already have these, Follow the CCB tutorial on creating this user by going to https://churchcommunitybuilder.force.com/s/article/How-to-Create-and-Manage-API-Users
Give your API user the following permissions.
Your site is now connected to CCB. You can now use the Page Builder to Sync your groups and events from CCB.