I am creating an object, and I need to put in indents for fitting other pieces in.
I go to extrude -> placement -> define -> then I select the face, draw the rectangle, but it won't let me dimension and change the size on my sketch.
Any help is great.
I can't open it because you are using schools edition unfortunately. It sounds like you might have use of the "symmetry" constraint. Take a look for that in the help file and perhaps this will help?
You can open it to view this model by using (for example) Creo View Express (http://www.ptc.com/products/creo/view/express/).
A screenshot of what is happening on your end might be helpful. Openning the file I don't see any problems like you're describing just an incomplete analysis feature.