To upload data into your shop you need to download the correct database format first. To do this you need to go to your admin panel and go to Tools>Database Import & Export and download either the Access or Excel spreadsheet that you wish to use. Then enter in the additional information into the appropriate fields taking into account the Database Update tips on the bottom of the Data Import / Export Page or the user manual.
Once this is complete, you can upload your data via the Import section on the Data Import / Export page on your admin. Be sure NOT to change the name of your spreadsheet or any columns, formatting etc.