To add a new field in a web form, you either go in to a web template you already created, or simply make a new. Add a new field from the list to the left.
Click on the fields that you want to add to the form. When you have chosen a field, you type in the description of the field. You can also choose if you want the field to be mandatory or not.
To add more fields, click on Add Next Field.
You can add as many fields as you want. When you are satisfied, press "Save Form"