Learn Hardcore Spanish (Latin America): Si la botella está casi vacía, agrega un poco de hielo dentro. - If the bottle is almost empty, add some ice inside.

In Spanish, real or likely conditions introduced by si take the present indicative. You’re talking about a real possibility (the bottle really might be almost empty). The subjunctive (e.g. esté) would be used for hypothetical or unlikely scenarios.

What verb form is agrega here?

Agrega is the affirmative tú imperative of agregar. For regular –ar verbs, the positive tú command is identical to the él/ella form of the present indicative (tú agregas → agrega).

Why choose agregar instead of poner or echar?

All three can mean “to put,” but agregar specifically carries the sense of “adding to what’s already there.” Poner is more general (“to place”), and echar often implies “to throw in” or “to pour.” The speaker wants to stress adding ice.

What does un poco de hielo mean, and why is hielo singular?

Un poco de hielo means “some ice.” In Spanish, ice is an uncountable noun, so you use un poco de (a little bit of) + the singular noun (hielo), not a plural.

Why is vacía feminine, and what is casi doing there?

Vacía agrees in gender with la botella (feminine). Casi is an adverb modifying the adjective vacía, meaning “almost empty.”

What part of speech is dentro, and why is it placed at the end?

Here dentro is an adverb of place meaning “inside.” Spanish often places adverbial phrases after the verb phrase or at the end of a sentence for clarity or emphasis.

Is dentro necessary? Could you just say agrega un poco de hielo?

You could omit dentro and still be understood, especially if context is clear. Adding dentro simply removes any doubt about where to put the ice.

Could you say dentro de la botella instead of just dentro?

Yes. “Agrega un poco de hielo dentro de la botella” is perfectly correct and more explicit. Native speakers often drop de la botella when the object is obvious.