Understanding Enterprise Integration Messaging Patterns

I'm currently reading Enterprise Integration Patterns: Messaging book.

But I've still difficulties to understand patterns and their applications, especially when looking at existing implementations such as NServiceBus, MassTransit and in another fashion RabbitMQ.

http://ift.tt/2lGmV2L

For example, in the Messaging Channels sections, there are PointToPoint, PubSub AND MessageBus but I don't really get the reasoning behind MessageBus vs other type of channels.

I'm trying to work on a custom implementation for both work and educational purpose, and while I don't want to get a full featured library, I'd like to it properly.

I could not find any materials on a simple implementation of each patterns (or at least the most common) and connecting them together.

For example, the purpose of the Endpoint I understand that it can be both a Receiver or a Sender so it means it can send(Message) or receive() but then, what is the difference with the MessageBus ?

So it means that I can subscribe to an Endpoint with subscribe(MessageType, Handler) ?

I also don't really see how it connect with Queue systems (such as RabbitMQ or custom SQL implementation).

Does Endpoint exchanges messages through a Queue by Enqueueing / Dequeuing from it? Does this happen in the Channel ?