Question

How would you command someone not to eat (comer), using the tú command?

Answer 1

We would say "No comas."

I can actually show you how we do it. It's pretty easy

1. Let's look at the infinitive: COMER

2. And now, let's conjugate it into the (Él/Ella/Usted) form: COME

You see how "Come" ends with an E?

Here's the big rule:
If it ends with E, change it to A.
If it ends with A, change it to E.

3. Let's change COME into COMA.

4. To make it a Tú command, add an S.
Now, it's COMAS.

5. Don't forget to start with the word "No."

So now, we have "No comas."