P for PROGRAM. Am I right or wrong. Manual Mode is for dummies!

[Bitter Jeweler]

I was trying a wide open/deep depth of field land scape shot.

Wide open/shallow DoF (low f/#'s)
Closed down/Deep DoF.(high f/#'s)

 

[Overread]

To add to Bitters summary have a play with this little program here:
Online Depth of Field Calculator

That should help you get a little bit more of an understanding for depth of field. It's not just the aperture, but also reliant on the focal length and the distance you are focusing upon.
Also don't try and memorize the numbers - just get a basic understanding of the principles and a lot of the rest you will find falls into place with practice, experience and also limitations at the time you shoot.

ALso a word of warning when you decrease the aperture (increase the f number) you will get more and more depth of field - however sharpness is also affected. For most lenses sharpness will increase (up to a point) as you approach f8 (some lenses are very sharp wide open - at say f2.8 or wider so the increase is far less noticable) however as you move beyond and toward f10 diffraction starts to take place within most lenses. Up to around 13 its normally not a both and f16 can also be usable (though I tend to avoid it) after that however whilst you are getting more and more depth in the shot the diffraction effect will start to soften your images no matter how well you take them.

The actual point where it becomes a problem is highly dependant on both the camera body you are using and the lens that you are using at the time and the above is only a very rough guidline.