You need to find out the IP address of the container running in the host so you can, for example, connect to the web server running in it.
docker-machine is what is used on MacOSX and Windows.
Firstly, list your machines:
$ docker-machine ls NAME ACTIVE DRIVER STATE URL SWARM default * virtualbox Running tcp://192.168.99.100:2376
Then select one of the machines (the default one is called default) and:
$ docker-machine ip default 192.168.99.100