connect to other virtualbox

[4fath]

I guess i need some help about networking on virtual machines.
how can i connect to each other ? let me explain my trouble
I am using win 8.1 and i have 4 virtual box . I install mongodb all of they. i wanna use as a host one of them and connect the host with the others.
How can i configure these ? should i use server or no need this ?

[mpack]

Have you read the user manual, chapter 6? That should be your starting point.