Save and open your Scratch program.
When you are ready to save your program, go to the Scratch menu bar, select File, then Save from the dropdown menu. Give it a name that describes what the program does (example: blinklight), and save it to your computer’s desktop.
To open a program you saved earlier, choose File, then Open, and select the file. Scratch files will end with .sb2.
Watch this video for detailed instructions.