Docker. How does it work?

I can find any number of guides to install and create docker containers. But I don't understand how to use them. Are they in the hosts $PATH and work like any other app or program ?Do they have internal networking, or like a container that I can bridge to my lan?

For example, mythtv seems like it could work in docker well. But how do I actually connect to it, start it, and so forth.

Ultimately I'd like to move everything I can into Docker. But I can't find how to actually use it beyond container creation.