How can I create a small text box inside a message box? I find some sites, but they confuse me lot. I have only made a message box, but dont know how to get the text box inside there. How is this done?
You can't use a messagebox for that. You have to create a custom "modal" dialog box.
This is nontrivial unless you're using some kind of GUI designer. Doing it "by hand" involves placement of individual controls and gets hairy pretty quick.
A MessageBox is a pre-made dialog box with limited functionality that is provided for convenience. They typically consist of message text with a Ok/Cancel button combo... or a yes/no/cancel button combo... or something else along those lines.
The amount of flexibility you have with a messagebox is limited. Whereas if you use a full dialog box, you can design it entirely how you want. The downside is there's more manual work you have to do to get it functional.