In the past, I've worked with Siemens Unigraphic NX software, but right now I only have AutoCAD 2010 Mechanical at my disposal. In Unigraphics, I was able to just go into a 2D sketch, make the basic shape of what I wanted, then add dimensions and constraints to the sketch and the lines would adjust accordingly. It seems like in AutoCAD that once I create a line, it is fixed at the length I created it at. Is there any mode I can use that will allow me to make rough sketches, and then use dimensions and constraints to set the appropriate lengths?
Try commands _GeomConstraint and _DimConstraint.
Also, if you use ribbon, you can find more functions in Parametric ribbon tab.