I have not used WF3 yet, but i do not think they have changed the way they do sections differently from
WF2, have they? If so, ignore how i tell ya how to do this then:

Before you do anything following. Make sure that you have an assembly datum where you want the section to go thru. In an Assembly it will only make the section on a assembly datum. You can create one before, or during the process. Sometimes it is easier to create it before.

1. Pick on the View Manager Icon (looks like a note pad with a camera infront of it)
2. There are 6 tags...3 top...3 bottom...on the far right there is one there called "Xsec"
3. pick on that one
4. If there are none already there you will see "No cross section" hilighted.
5. Pick on the "New" button.
6. In the menu list another name will show in a dotted box and it will be Hilighted. You can type in the letter, number, name or however your company labels the section here...example : A
7. Right click and it will take you to the "sec opt" menu. ( i will just be telling you about a normal planed section here)
8. Pick "Done"
9 Then the "Menu Manager" opens up and gives you 3 choices"

Plane
Make Datum
Quit Plane
If you have already created your asm datum. then just hilight "Plane" and pick the plane you created. And it will quickly make the section. I will not show it to you at that time.
If you have not created your asm datum, Pick on the "Make Datum" and you then will create the datum that you want and when completed that pick "done" and the section will be created.
Again, It will not show it at that time.
It will show in yellow where the section is, but will disappear and go back to the view manager.
Where you can double click on the section you created. The red arrow will move to that section and your model will be sectioned in the Main view. It will stay that way until you double click on the "No cross section" and then the section will go away.

Hope that helps. Again. that is for WF2. But i don't think it changed. If it did let me know.

smooth