Download both files, put them in a folder and run the GroceryStoreTester.java file in an ide or on terminal.

To open in a terminal, type in "cmd" into the location/address bar at the top of the window in your folder and press enter. Now that terminal is open, type "javac GroceryStore.java" and press enter and then type "javac GroceryStoreTester.java" and press enter again. Now to finally run the file, type "java GroceryStoreTester" and the program will run.

Make sure you have JDK installed, install it here: https://www.oracle.com/java/technologies/downloads/#jdk21-windows