It just needs to be a CSV file not Excel (.xls), with the first row making up the headers
You upload and are then offered a form to map your columns with what the plugin is interested in…
First name, last name, gender, date of birth, email, cellphone, landline, address (as one column or street address, city, state/county, zip/post code), small group, member type
You don’t need to supply all the columns, but the more you do the more powerful the import is!
The plugin will sort people into households by address and the first named at an address is assumed to be the head of household.