Visitor fields are set per button. This means you can set up different fields for different types of visitors based on their button selection. Not all buttons allow you to use Visitor Fields, but most do.
Start on your Buttons tab on the left of your account dashboard. Select 'Existing Buttons' on the right then click to edit (or add a new one) and scroll down to the Visitor Fields section. You'll see you can 'Add a Field', or you can edit the fields automatically added to each button.
You'll see that there are a few customization options. The first line, "Hi There, what's your full name?" will appear with the field for visitors to see. The second line, "Type your full name," appears in the field to prompt visitors as they begin typing. Both of these labels can be customized, allowing you to create the field of your dreams... License Number, Favorite Super Hero, etc.
You can select the three dots on the left of each button to drag and reorder them. And the lock icon allows you to choose whether or not the field is required (please note the 'optional' setting is not currently available for yes/no field type).
You can view all information collected from your visitors via the Visitor Log. Name and company are immediately apparent. Additional fields can be seen by clicking anywhere on the line of that visitor; this will open the visitor's details, including additional fields, NDA signature, etc.