How to change the Graphics Dynamically in android.

hello sir
         currently i am working on android platform(Tiny 210,android 2.2).
and i would like to draw graphics on android. and Change that particular
graphics on user input(DYNAMICALLY). the change like length, angle(All
angle relevant with graphics), width,view .

i refers through the android book,android site(developer.android). but i
can not understand how "TO USE A CANVAS". so please provide me guidance.
i have some doubt 

1. It is necessary to Implements the canvas in another activity?
2. how to use thread to implement canvas.
3. which are the method use for it.
4. provide me a flow to implements the canvas.