This might help understand the players: http://www.lumapartners.com/resource-center/lumascapes-2/
I knew nothing about ad-tech when I started my startup and Charles is right that it is a confusing industry. I have been at it over two years and I am still trying to wrap my head around it. Get ready for a ton of acronyms, confusing jargon, and multiply words for the same thing.
Go to http://openx.com/ and then click resources and it will help you start to learn.
As for getting signed up with exchanges... The tricky thing here is they want you to have volume before they will bother signing you up. (as in number of unique visitors per month) It is a chicken and the egg thing. If you have volume then signing up is easy but if you were making ad revenue then you could grow your volume.
Exchanges didn't give us the time of day until we signed our first partnership with a company that had 1.6 million unique visitors per month. Which meant we would be doing about a 10 million video ad impression a month. Then it was as simple as going to the contact page of each exchange's website and asking to to speak with.
Example: "We have 1.6 million unique visitors and are looking to do about 10 million impressions a month. Who do speak to about using your exchange, ad server, fill in the blank."
So that is how we have stumbled are way through the industry so far. Hope this helps.