As thedestro said, one nation sends you money in exchange for you sending them technology. A middleman is not always required. You will need open aid slots to transfer the funds. You can increase the amount of money you collect with improvements, wonders, random events, donation deals, ground attacking other nations, increasing your working citizens by purchasing more infrastructure, land, or technology, et cetera.
You can check out the Black Market section of the forums here: http://forums.cybernations.net/index.php?showforum=62 to offer to buy or sell technology. There are other means of finding deals outside the forums, including alliance forums, IRC, and or in-game private messages.
http://www.cybernations.net/video/CN_demo.htm At frame 51/55 it will show you where to click; you view another player's nation and click on Aid.