If it does make a difference, as in a form to order things from an online shop, you should use post. Handling Form processing takes place when the browser submits the form to the server. Processing reads and checks all the data entered and stores it in internal data format. Afterwards, the action associated with the button is executed. Form processing takes place during the initialization phase of the page, i.e. before anything is displayed.
Error handling is crucial.
If the user entered wrong data into a field, form processing notices this and redisplays the form with an appropriate error message. The action associated with the button is not executed in case of an error. Note that this works differently compared to native HTML forms. From an HTML view, RAD page forms always have an action pointing back to the page containing the form. This is required to redisplay the form in case of an error.