How do I make the HDMI connection between my MacBook and HP 22eb display work?

I have a new MacBook; the salesman suggested buying a non-Apple monitor to save money. I bought the apple HDMI cable. I bought an HP22eb display to use on my desktop for a larger screen. When connected, I get my screen saver, but no other functionality. There is no users guide, nor does HP answer support! It must be something simple that I am doing wrong. Frustrating!