Great questions! Let's start with the Lightning Network. It's a second layer on top of Bitcoin that allows for fast, cheap transactions.

And yep, it's decentralized! The network is made up of nodes and channels between them. Anybody can run a node and open channels - no permission needed!

As for how many there are... well, there's only one Bitcoin network and one Lightning Network. But within those networks, there are thousands (even millions) of nodes all working together.

Remember though - while these secondary layers offer benefits like speed and low fees, they also come with their own set of challenges to tackle. Always important to do your homework before diving in!