How to connect 2 MS Exchange Server ?

Pls Help,
I have 2 Exchange Server 5.5,
I don’t know how to connect the 2 Exchange server on 2 different win2k domain controller, on 2 different domain, on 2 different organization1 and organization2, on 2 different site1 and site2.

I want my 2nd server to route outgoing message to 1st server and receive incoming mail from 1st server.

Will somebody help me pls??