How To: sql insert with a plugin when creating a page

I want to create a plug-in that adds some elements to a page. I have figured out how to add the element to the actual page.

This element is a check box. When an author writes a page I want them to click this check box to indicate if this is a page of one type or another. I want to then add that to what is written to the database.

So, I understand the logic of it, seems pretty easy. I cannot for the life of me figure out how to WRITE it. How do I write the function that will add the check box value to the insert that the “save post” button does? I have already set up the db. That was easy.

Any one have any ideas?

Thanks.