To edit a question, select it from the middle column by clicking on it. If you want to re-arrange the order of the questions instead, just click and drag the input where you want it.
On the right column, the settings panel for the selected question is activated when clicking on a question. Perform your edits here.
The formbuilder validates questions automatically most of the time, just by interacting with it.
If you would like to force validation on the selected question, click the validate button on the top right of the settings panel:
A valid question can be copied to the bottom of your question list by clicking on the copy button:
A question can be deleted by clicking on the delete button:
If it happens you make changes by mistake, do not worry. Just do NOT save, but click on the UNDO button instead:
All the questions for a form can be deleted at once, without deleting the enclosing form.
Select the form and click on the "Delete all questions" button in its context menu.