Docker: How networking works for Docker and how many interfaces can be created for a docker container ?

Question

There are multiple cases:
1. A number of containers have been launched in the same host. how these container communicate to each other
2. Out of "x" numbers of containers in the same host, I want to enable communication between two specific containers. How I can achieve this ?
3. Containers have been launched into different hosts machine and I want to enable communication between these containers. What are the options available ?