You start writing at the beginning. Break it down into steps. In my early days, I would do the steps at first that were easy, then leave gaps in the code where I knew I had to add something. In a gap, I'd type some random, unexecutable string that I knew MATLAB would fail on, so my code would not run until I filled in all of the gaps.
Then I'd fill in each gap, one at a time. As you are writing it, take a piece, execute it as a code fragment at the command line. Verify that it does as you expect it will.
But sorry, you need to make the effort. This is your homework, not ours to do. When you actually have a question about MATLAB, as opposed to asking us to do your work, then ask it.
