I am not sure I understand the question, but you can call a UserForm anytime
from any code module because it is a separate object. But if it is already
visible you cannot open a second instance of it. The TextBox has a double
click event that could be used, but not a single click. There are other
events such as enter and exit that could also be used to call a userform.
You can view these events by creating a textbox from the Control Toolbox and
then right click the testbox and click view code. Click on the declarations
pane to get the drop down menu of all the events for the control.