Welcome! By the end of today, something on your screen will move because you told it to. That is programming, and you are about to do it.
What programming really is
A computer is fast, obedient, and completely without imagination. It does exactly what it is told, in exactly the order it is told, and never guesses what you meant. Programming is writing instructions so clear that a machine with no common sense can follow them.
Think about telling a friend how to make tea. "Make tea" is enough for a human. A computer needs: fill the kettle, switch it on, wait for it to boil, put a teabag in the cup, pour the water, wait three minutes, remove the teabag. Every step, in order, nothing assumed. That habit of thinking — small steps, right order — is the real skill of this course.
Why Scratch
Most programming languages are typed as text, where one missing semicolon or misspelled word stops everything. Scratch, made free by the Lifelong Kindergarten group at MIT, replaces typing with blocks: coloured shapes you drag and snap together like Lego.
- Blocks only fit together in ways that make sense, so you cannot make a spelling mistake.
- You can click any block at any time and immediately see what it does — no waiting.
- Your program is running while you build it. Change something, and the change happens live.
Scratch is not a toy version of "real" coding. The ideas inside it — sequence, loops, conditions, variables, events, data — are exactly the ideas inside Python, JavaScript, and every other language. You are learning the thinking; the typing comes later and comes easily.
The two things you will meet today
- A sprite is a character or object in your project — the cat, a ball, a spaceship, a slice of pizza. Sprites are the things that do stuff.
- The stage is the white rectangle where sprites live and perform. It is your theatre.
Every project you make in the next twelve weeks is sprites doing things on a stage because blocks told them to.
Try it now
Open a browser and go to scratch.mit.edu, then click Create. Say hello to the cat — his name is Scratch Cat, he has been on that stage since 2007, and he is about to become the hardest-working actor you know.