Connections
Each pair of web applications must have two Replication Connections. Replication Connections specify how one web application will talk to the other and also ensure each web application is authorized to communicate with the other.
As SharePoint content is being replicated between web applications, the Replicator instances for each web application are actively communicating with each other and delivering status updates. This is why each web application in a pair must have an outbound and an inbound connection to the other web application.
Map Families
Map families define what SharePoint changes will be automatically replicated and how often that replication will occur. In most cases, there is only one map family defined for a Replication Network, but there are also valid reasons for having multiple map families.
When you create a map family, you specify its scope. The scope determines which events are available to capture. You should select the scope of your map family to represent the events you want to capture. For example if you want to capture and replicate new site collections, then you must create your map family with a Web Application scope.
Queuing and Capturing Events
Queuing and capturing are two different ways in which SharePoint events are replicated.
Queuing
When you with Replicator, you are manually selecting what you want to replicate. Replicator goes through your SharePoint environment, at the levels you specify, looking for items that match the events you queued, for example list item updates. Queuing is useful for initial replication scenarios or when you want to manually promote content from one site to another, such as intranet to extranet or development to testing. With queuing you can replicate the entire contents of your web application to another web application so that they are consistent from the start, even before live replication starts.