To write a MATLAB program or script, you can follow these steps:

1. Open MATLAB: Firstly, open MATLAB software on your computer.

2. Create a new script: Click on the "New Script" button in the Home tab or use the "Ctrl + N" shortcut to open a new script.

3. Write your program: Type the MATLAB commands or code that you want to execute in your program or script. Make sure that each line of code ends with a semicolon (;) unless you want the output to be displayed on the screen.

4. Save your script: Save your script using the "Save" button or use the "Ctrl + S" shortcut. You can choose the location where you want to save the file, as well as the name and file extension (.m).

5. Run your program: Click on the "Run" button or use the "F5" shortcut to execute your program or script. You can also type the name of the script in the Command Window and press Enter to run the program.

6. Debug your program: If your program encounters an error, MATLAB will display an error message in the Command Window. You can debug your program by identifying the source of the error and correcting it.

7. Modify your program: Once you have written and tested your program, you can modify it as needed. You can add new commands or change the existing ones to improve the functionality of your program.

8. Repeat steps 5-7 until your program works correctly: Test your modified program by running it again and making sure that it works correctly.

By following these steps, you can write, test, and modify MATLAB programs and scripts to perform a wide range of tasks.