How to draw some points and lines?

I'm a freshman in Qt programming, so I know this question is too simple but I want some guides. And I am using Qt3.
I want to develop a small application. And I want to make the user interface(maybe a dialog) within Qt Designer and then add my own code into it. The major function of the application is to draw some points and connect these points with some lines, e.g. push one button on the dialog to invoke some slots to draw some points and another pushed button will invoke to draw lines connecting these points.
So my question is which class or widget should I use to draw these points and lines on it in my dialog?

Can I just drag a predefined widget on the dialog and directly draw on it? If it is possible, What kind of widgets shoul I use?
Or is there any appropriate example in the documents provided by Qt Assistant
Thank you.

See the scribble and drawlines examples that come with Qt.

And, please, don't post the same question in multiple threads.