How does HTML Canvas Works?

Hi, I know this question probably already exists on the forum but the truth is that I have never been able to find something right, and WiseJ (in my opinion) doesn’t explain very well how it works, I’d like to get some code that goes straight into this Subject. I need a button that after clicking takes a screenshot of the FORM. Very simple, I’m also a little new to WiseJ, but I find the library a little confusing and the docs even more so. If someone can help me in this aspect I would be very grateful.

Im programming at VB.NET , if someone could provide the code at VB.NET would be awesome!