Files are in Comma Separated Value(CSV) format. This is widely supported and any spreadsheet should be able to export in this format. The rules vary slightly, depending on whether or not the import of Test Users is selected.
The supported fields are:
The user's name, e.g. "Alice" or "John Smith".
The user's email address. If importing Test Users, then this email address is stored for later use (if the user is converted into a real user).
A message to with the invite. Not relevant for Test Users.
A "suggested" username. If not supplied a suggested username is auto generated.
name, suggested username, email, invite message Paul, paul, paul@test.com , Hi Paul John, , john@test.com Alice , alice, alice@test.com