Click on Create New button to create new nagivation group. Once you create a navigation group, You can create navigation custom fields or navigation links.
Create / Edit Navigation group details
On Edit nav group, You will see one more tab here for custom fields.
How many level of childrens you want into the menu? (min 1 to max 5)
Navigation Fields.
You can add navigation fields once you create the navigation group. Navigation fields will be different for all the navigation group. So if you want the same field to show in all navigation group, you have to create that field in all navigation group.