Qt - What to use for a text box

If with text box you mean it one line then it should be QLineEdit.

Anyway I suggest you to get a look at some full working samples to learn using all available widgets.

QLineEdit for textbox

QTextEdit for textareas

QPushButton for buttons

Here's the complete component reference: http://doc.qt.digia.com/qt-components-symbian-1.0/qt-components.html