web control on hidden textbox

[newbeee]

I have a bunch of txtboxes that need to be fill with data from a listbox when user click on it each listbox item. Here's the scenario:
1. user click on a txtbox
2. user click on an item in a listbox
3. txtbox populate data from user selected item

However, this can't be done using windows control, it'll have to be done using web control. I'm not very familiar with web control, does anyone has any suggestions?

I heard that you could use something like a hidden input that store textbox state (the textbox that was last clicked or active), then assign that hiddenbox control value to be listbox.selectedvalue.tostring and populate that into the actual textbox?

I don't know much about web control or javascript. Any examples or thoughts are greatly appreciated.

Thanks.