If you don't know what a .csv file is your aren't alone. (.CSV) file is a formating found in Excel. If you look below you will see a series of excel spreadsheets all in different formats. 

 

In order to load a spreadsheet into MonsterConnect it needs to be in .csv. 

If your file is not in .csv, simply open the spreadsheet, click file save as and change the "save as type" to .csv"