Hmm, reading the Survival Guide is still a good idea, but I don't think the answer to this question will depend on what OS or version is being used
Here's a first step:
1) File > New > Drawing (get a blank-paper window: OpenOffice.org Draw)
2) Click on the "Line tool" icon (bottom of the Draw window, second from left; looks like a diagonal straight line)
On the "paper", the mouse pointer will look like a "+".
3) Click anywhere on the paper, hold the mouse button and drag.
4) Release the mouse button: a straight line will be added to the drawing.
I don't think the Draw Guide is on the web yet, but you can get a PDF here: OOo Guides