Radius - This is for farming an area around a particular address. Just enter your center point address and then select the number of cards you want to send from the dropdown list.
List - Upload your own list in either a CSV or EXCEL file. Other file formats will not work. There must be a minimum of 50 contacts. Field order does not matter but you should make sure that each part of the address is in a separate field, ie first name, last name, street, city, state, zip should all be in separate fields all on one row.