"¡No comas eso!"
Translation:Do not eat that!
in positive commands you use "come!" that is right. But the negative conj. of commands is exactly the same with "subjunctive tense". comer in subjunctive comes like "coma,comas,coma,comamos,coman ..." so you use them while forming negative commands. "No comas!-do not eat! ; No comamos! - Let's not eat! etc. :)
Indicative vs Subjunctive
The indicative expresses certainty, objectivity, and is based on factual information. We use this tense to declare something.
The subjunctive mood expresses uncertainty, personal emotions or wants, and subjectivity. We use this tense to avoid declaring something.
So in this sentence 'Do not eat that' sounds like a 'want'. Is not a want an imperative?
The imperative mood is used to tell someone to do something in a direct manner, or simply, a command. For a softer command, the subjunctive is often used. Because Spanish has two ways to address someone directly based on formality (tú and usted) there are two different manners in commanding these people.
(excerpts from Spanishdict.com
Some of this stuff in beginning to sink in. Two moods. IMP and SUBJ, and each has their present/past/future etc tenses. With corresponding word spellings. Luckily the words have small changes in the last letters that will trigger your brain. Those conjugation charts are growing!