You would use the "click" or "AfterUpdate" event of the checkbox. In the
property sheet of the checkbox find either of these events, and set it to
"Event Procedure", then click the ellipsis (...) next to the event box to
open up the VBA editor. Then enter the appropriate code into the editor.
You say that you want to disable a text box when you click on the checkbox.
I doubt this is what you really want, and assume that you want the text box
enabled if the checkbox is checked (true), and disabled if the checkbox is
unchecked (false). If this is what you want then the code is:
Me.NameOfTextBox.Enabled = Me.NameOfCheckBox
(Obviously you replace NameOfTextBox and NameOfCheckBox with whatever you
have called the controls).
If you want to do exactly what you said then the code would be
Me.NameOfTextBox.Enabled = False
