As Chicopee said, learn how to use the OSNAPs. If you want to draw a line from the center of a circle to any point on the circle, type the following (<SP> = Space bar):
LINE<SP>CEN<SP>
Bring the crosshairs over the circle somewhere and a blue box or diamond or circle will appear. Click. AutoCAD has the center.
Then type:
NEA<SP>
Bring the crosshairs near where you want the line to connect to the circle. Click again.
There are a variety of OSNAPS:
NEA - Near to
END - End of
CEN = Center of
MID - Middle of
INT - Intersection
to name a few. There are more. If you will be working with AutoCAD 2012+ a lot, learn how to turn on "Running" OSNAPS.
As far as "Reference" lines or dimensions, I'm not sure what you mean.
If you mean non-printing entities only visible on the screen, create a layer for them and make the layer a non-plotting layer. If you go into Layer Manager you can make a New Layer. Do this in model space. In the Layer Manager there is a column that permits you to toggle a layer to be non-plotting. Click on the symbol in that column for the layer you created.
If that's not what you mean, please explain.
Ralph
Structures Consulting
Northeast USA