Trouble with second monitor display?

I bought an external monitor for my mbp..

I do NOT have it on mirror display. However, I have my external monitor as my main monitor, with the dock dragged over to this screen as well. It's connected via HDMI. This is the problem I'm running into:

When I maximize a screen on the external monitor, it maximizes as it should. When that happens, my mbp screen turns to that thatched-looking grey screen. If I use my gestures on my wireless trackpad to swipe back, the external monitor will go back to it's desktop in order for the mbp screen to have a desktop photo on it. Basically, I can't see two different things at once with having dual monitors..

If I drag something over to my mbp screen, I have to be at the desktop on my external monitor in order to do so, and when I do, the external monitor goes to that thatched-looking grey screen. So again, I really can't look at two things at once when maximizing aplications.

the only pain in the arse temporary thing I'm doign right now is just draging the margins to fit the dimensions of the screen, and not the 'double arrow' icon in the top right to maximize it.. and try to juggle btwn different windows I open that way.

Huge pain.. not as efficient and I planned on.. Please help me with this issue!

Thanks in advance! Jon