Gai,
Thanks for trying to help a newbie to you and all. However your answers are not detailed enough to work. Lets take this a step at a time. I downloaded your example so I have on my screen the oval cylnder.
You wrote:

1. make a flat plane at 90 degrees ---> How do you do this? 90 degrees to what axis??

2. position where you want the cut - use "move" tool.

      Gave up on step 1 and used your pre-made oval shape.
      First question: position what? the Move cursor I assume you mean.
      OK, I positioned it on lower right corner of the shape and clicked once.
      I get strange actions here. Sometimes it does nothing, or leaves a point or 
      forces the shape to expand or contract when I move the mouse, etc. Junk.
   

3. Rotate to desired angle - use the rotate tool.
   The rotate tool gives me a protractor with angles listed in lower right hand corner of screen. Now I click when the cursors says "on edge" since I want to section in a vertical plane. Then the cylinder shape just tumbles randomly when I move the mouse.

I give up. This is not an easy tool to use at all.

I can draw this easily in Visio but it is 2D. Attached is another description of the problem.

This Sketch Up is driving me nuts. The first simple thing I tried to draw is an oval.
I have no idea how to do this. There is no oval listed. A search of this forum and Google shows now way to do it. Even the on-line Google help is of no use.
Here is what I am trying to do:

1. Draw an oval
2. Stretch it into a 3D long oval shape (like a cylinder, only oval).
3. Cut a section through it at 5, 10, 15 and 20 degrees to see what
   the cross section looks like.
   Any ideas???