In need of help, desperately. VB coding help needed.

I want a code in which I can draw a STRAIGHT line with my mouse, from point to point on a picturebox. I need a code in which I can click on one place in a picturebox and click another point in the picturebox and it'll create a straight line from there, I want to be able to access this with a button. So, if I click a button it does all this ^^, but when I click on a different button, it stops doing this. I'm trying to make a paint program, basically, just not entirely. Help me out?

-Thanks