How do bots to communicate in a botnet?

I see this post : How do bots communicate in the zeus botnet? but this post doesn't responding really to my question.

I'm really trying to understand how a bot can communicate with a C&C. Technically I know that bots used sockets for example. But I really have no idea how the C&C can send command to a bot/computer which is probably inside a LAN private network. Lots of computers are in a LAN behind a box, or a router. So for communicate behind a port with a server you must to use NAT I think. So if anonyone have information about it, I take it.