Waste can be a bit of a process to set up. We went through the whole process a few months ago in
this thread, and then some of us started a few secret networks. It's a long read but everything you need to know is there. Give it a chance, 'cause as far as I know it's the only program that fits your request. Take a look at
Filetopia too. It's larger and more open than Waste so it might not be so easy to set up a private network, but I've never used it so I'm not sure.
As to your question, you have to put in the IP address of the person you want to connect to, and before you do that you need their public key and they need your public key. In the Private Key section of the Prefferences dialog you can export your public key so you can email it to the other person.