Add an admin option for my Plugin

Hello,

I have written a simple plugin, that will add certain information to pages / posts. I want this information to be integrated into posts & pages only when an option is selected from within the admin post / page editing area.

I have everything for the plugin written with the exception of the post / page editing area check-box option.

My question is – How do I add a check box – in the post / page editing area – so that when it is checked, my function is called to echo the information?

Any help with this is very much appreciated.