Sometimes when you're adding a new family to your system you don't want to type the contact information over and over. Koha allows for you to duplicate a patron and change only the parts you want to (or need to) change.
Open the patron you want to use as your base (the patron you want to duplicate information from)
Click the 'Duplicate' button at the top of their record
All of the fields with the exception of first name, card number, username and password have been duplicated. Fill in the missing pieces and click 'Save'
Clicking in a field that is already populated with data will clear that field of all information (making it easier for you to type in something different)
You will be brought to your new patron