First you have to create an object from the HighscoreManager class, we will call it "hm" in here.
Afther that you can add scores by using the .addScore() method. The first parameter has to be the name of your player and the 2nd one is the highscore (as an int).
You can print the getHighscoreString function to get the highscore in String-format and display them on the console with System.out.print()
Note: the first time you run you will get a "FNF Error", this means that the program hasn't found the highscore-file, this is logical because we haven't created that, but you don't have to worry, Java will create one itself, so afther the first time you won't have the error anymore.