UNICOM Intelligence Developer Documentation Library comes includes a sample spreadsheet you can modify to suit your needs. It contains basic documentation about how the spreadsheet is set up and which columns you must create. The file is called UsersAndRoles.xlsx and it is normally in:

The Excel spreadsheet can have any or all of the following worksheets: Roles, Users, Projects, Activities, UserProperties, and GlobalFilters. If a worksheet does not exist then that part of the import process is not run. The worksheets must be set up as follows: