UNICOM Intelligence Developer Documentation Library includes a sample spreadsheet you can change 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 this folder:

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, that part of the import process is not run. The worksheets must be set up as follows:

If a column contains text values that are longer than 255 characters, put the longest values in the first row. This is because the import process decides the length required for each column based on the first few rows of the spreadsheet.