I think I'm really confused about how a web page works with respect to control event.s

I have a textbox on my page. I want to know when the user changes something, so I dbl-clicked the TextChanged event - which
doesn't fire unless the Texbox tag has the attribute AutoPostBack = "true" in it. At least, this is what's happening in my page.

This of course causes the entire page to be reloaded.

This is really screwy. I gotta be doing something wrong.

What if I want to collect data from 3 different textboxes, THEN send it all to the server. But I want to know when any field was
changed? I'm not interested in firing off to the server when the user types, I just wanna know that they did type.