On the start form, don't modify the value of either field, and click the Submit button. Check the value of the process variables, and notice that they have the default value.
Now modify the value of the text and date fields, and click the Submit button. Check the value of the process variables, and notice that they have the values you entered.
If you do not see the value you entered, make sure that you selected the Parameter checkbox when you created the process variable.
To see what happens when the default value is incorrectly configured, remove the default value from the process variable definition. Then update the expression and set the value parameter of the text component to ="Default text from the component". View the form and submit without modifying the text field. Notice that the corresponding process variable does not have the default value.