How can I add a field to my form?

3- How do I add additional question information to the form  i already made?

Yes, it is possible to add a question to your form no matter if it has been already created, to do it, you only need to click on your form and the edit form button: 

Once in the Form Builder you only need to click on the "Add Form Element" option, drag the field you need to add and drop it where you want it to be, here's also a screen-cast about it: 

Hope this helps.