You can also just make a little very simple schema of what you want ( a little part) and someone show you with a little tut video
(made with the free wink http://www.debugmode.com/wink/ for example) or a little image how make your piece :)

And for the "measure" you have a very tricky system of helpers for draw anything by rapport to anything :)
Just "click and move" and that draw the helpers with the function in use!

So when you have a circle you can draw it by rapport to anything yet existing in the screen!

Now what do you want exactly?