How do you create commands (imperatives) in Spanish?

There are two basic forms of imperatives, negative imperatives and positive imperatives, and these can be divided into informal (tú) and formal commands (ustedes/ vosotros).

Let's start with the positive imperatives in the informal 'tú' form. These are the easiest, as you just take the 3rd person form of the verb in the indicative. For example, hablar (to speak) becomes habla! (speak!). Comer (to eat) becomes come! (eat!). Some of the irregulars in this form of the imperative are decir (di), salir (sal), poner (pon), and tener (ten). 

Negative, informal imperatives become subjunctive. Don't speak would become No hables. Don't eat would become No comas. 

The subjunctive is also used for both sets of formal commands, positive or negative. Hablar is either hable! or no hablen! and comer becomes coma! or no coman!

That means you must know the subjunctive well to deal with commands, because all the irregulars stay the same, like ir would be no vayas! in the negative informal imperative.