Dynamically Populating Form?

I have a form to add items to a database. In the sidebar next to the form I have a bunch of pre-defined items, I would like to be able to click on one the pre-defined items and have it add a populated text field to the form. Any ideas, I am not quite sure where to start. Any help would be greatly appreciated. Thanks.

hi,
could you give more details, then I can help you