1)

If you are asking how in a Dynamic Form you can change the text value on the 'submit' button, then go to module configuration in the control panel and then go to 'Submit Link/Button'.  There you can change the text from 'Submit' to anything you wish. 

2)

If you are talking about a default value for the field then in Advanced Field Options there is a default value you can supply to a question.  That value will go into the text box to the right of the question.  
3)
If you are asking how the HTML dynamically changes from one message to the other when the radio buttons at the bottom of the demo are selected in demo 32 then that is done through javascript. What we are talking about here is a button to select purchase of Dynamic Forms versus a button to purchase the DataSprings Collection and based on the button selected a literal value is applied to the HTML control.

This is done by going into the Advanced Field Options and in the Client Side Events place the proper JavaScript code. Use an If-Else statement in JavaScript to do the following:

$(SubmitButton_Field).innerHTML = "Submit and purchase Dynamic Forms 3.4";

or apply the following value,

$(SubmitButton_Field).innerHTML = "Submit and purchase Data Springs Collection 4.0";

You can see that the submit button field is an HTML control that is mapped to the $(SubmitButton_Field).

If you need help with doing these things for your application then our premium support services can be used for supporting you in this area.

Thanks