Connecting with friends? [Steam]

Sorry if this has been asked before!
I'm trying to play with a friend on steam, but as we can't invite each other (why not?) all we can do is host and hope the other person can see/find it! and we haven't had any luck there either! Help!

This is pretty strange that anybody of you have problems with finding each other games because they all are hosted on Uber servers (and not your computer) and should be available in "Ubernet Games" list.