Custom connections are recorded via the green Add option displayed within a module's profile page.
After selecting Add, an Add Connection window will populate.
The contents displayed will vary depending on the title of the connection, the addition of any custom categories and fields defined within the control panel, and the other module name which the connection is related to. Any custom fields associated with the connection can be filled out while creating the connection by clicking on the tabs at the top of the window. These tabs represent the custom categories created within the control panel.
In example: if Attendees is the defined custom connection and there are custom fields set up against that connection type, the fields will appear within their defined category heading next to Standard Details. If custom fields are not assigned to a category, they will appear within the Other Data tab.
After populating the necessary information and selecting Save, the connection type appears within the contact's profile page under the Contact's tab. Seeing Viewing a custom connection for more information.