unable to understand bgchaindb behaviour?

I started to implement bigchainDB.I have followed the tutorial from here

I have setup two nodes running bighchainDB server running & also mongoDB. I have added node id and address of nodes to each configuration so that they can connect.I am able to create transactions on each node.So my questions are as follow

1. How two nodes communicate and sync data with each other.
2. How consensus is achieved ?
3. Why this tutorial is created for setting up cluster ?

BigchainDB nodes communicate with each other using Tendermint P2P protocol. Consensus is Tendermint consensus. To understand those better, here are some starting points:

• The BigchainDB 2.0 Whitepaper
• The Tendermint website and docs

Also, please ignore the old docs for versions of BigchainDB Server older than 2.0.0x.