Cierra bien la cremallera del abrigo antes de salir.

Yes. Cierra is the tú imperative of cerrar, so it means close in the sense of giving an instruction to one person you address informally.

• cerrar = to close
• cierra = close! / shut!

So Cierra bien la cremallera... means something like Make sure you close the zipper properly...

If you were speaking more formally in Spain, you would say:

• Cierre bien la cremallera del abrigo antes de salir.

If you were talking to more than one person in Spain:

• Cerrad bien la cremallera del abrigo antes de salir. (informal plural)
• Cierren bien la cremallera del abrigo antes de salir. (formal plural)

Because cerrar is a stem-changing verb in some forms.

The infinitive is:

• cerrar

But in the tú imperative, the stem changes from e to ie:

• tú cierras = you close
• cierra = close!

A useful shortcut is that the affirmative tú command usually matches the él/ella/usted present form:

• él cierra
• usted cierra
• tú command: cierra

So cierra is the correct command form.

Here bien means well, properly, or securely.

So Cierra bien la cremallera is not just Close the zipper, but more like:

• Close the zipper properly
• Zip it up well
• Make sure the zipper is fully closed

Spanish often uses bien in this kind of everyday instruction to emphasize doing something correctly or completely.

Spanish often expresses this action more literally:

• cerrar la cremallera = to close the zipper

In English, we often focus on the garment:

• zip up your coat

In Spanish, both ideas are possible, but cerrar la cremallera del abrigo is very natural and clear.

You may also hear:

• Súbete la cremallera del abrigo = Pull up / zip up the zipper of your coat
• Abróchate el abrigo = Fasten your coat

But cierra la cremallera is a straightforward and common way to say it.

Yes. In Spain, cremallera is the standard word for zipper.

So:

• la cremallera = the zipper / zip

In Latin America, other words may also be used, such as:

• cierre
• zíper / zipper in some countries

But for Spanish from Spain, cremallera is the safest and most standard choice.

Because de + el contracts to del.

So:

• de el abrigo → del abrigo

This is a mandatory contraction in standard Spanish.

Examples:

• la puerta del coche = the car door
• el color del vestido = the color of the dress
• la cremallera del abrigo = the coat’s zipper / the zipper of the coat

A similar contraction happens with a + el = al:

• Voy al parque = I go to the park

Spanish often uses the definite article (el, la, los, las) where English might prefer a possessive like your.

So in a context where it is obvious whose coat is meant, Spanish naturally says:

• la cremallera del abrigo

rather than:

• tu cremallera del abrigo
• la cremallera de tu abrigo

Those versions are possible, but they sound more explicit. Spanish often avoids possessives when the owner is already clear from context.

This is very common with clothing and body parts:

• Lávate las manos = Wash your hands
• Ponte el abrigo = Put on your coat
• Cierra la cremallera del abrigo = Close the zipper of your coat

Abrigo usually means coat, especially an outer garment for warmth.

It is generally more like coat than jacket.

Some related clothing words:

• abrigo = coat
• chaqueta = jacket
• cazadora = short jacket
• anorak = parka / anorak

So la cremallera del abrigo most naturally suggests the zipper of the coat.

Because antes de is the normal structure before an infinitive.

• antes de + infinitive = before doing something

So:

• antes de salir = before leaving / before going out

More examples:

• Antes de comer, lávate las manos. = Before eating, wash your hands.
• Antes de dormir, apaga la luz. = Before sleeping, turn off the light.

If a full clause follows instead of an infinitive, Spanish often uses antes de que + subjunctive:

• Hazlo antes de que salgas. = Do it before you leave.

Because after antes de, Spanish uses the infinitive when the subject is understood and the action is general or refers to the same person.

So:

• antes de salir = before leaving

You do not need a conjugated verb here.

Compare:

• Cierra bien la cremallera antes de salir. = Close the zipper properly before leaving.
• Cierra bien la cremallera antes de que salgas. = Close the zipper properly before you leave.

Both are correct, but the first is simpler and very natural.

As for salirte, that would mean something different, because salirse is a pronominal verb with meanings like to come out, to go out of place, or to leave unexpectedly in some contexts. It is not what is needed here.

Yes, in some contexts you could say:

• Sube bien la cremallera del abrigo antes de salir.

That would mean Pull the coat zipper up properly before going out.

The difference is subtle:

• cerrar la cremallera focuses on closing it
• subir la cremallera focuses on the upward movement of zipping it up

If the zipper is currently open at the bottom and needs to be pulled upward, subir is very natural. If you just want the general result, cerrar works very well.

In most of Spain today, ll is usually pronounced the same as y. So cremallera sounds roughly like:

• kreh-ma-YEH-ra

A more careful breakdown:

• cre = like kreh
• ma = mah
• lle = roughly yeh
• ra = a light tapped r

The rr sound is not in cremallera; it has only a single r at the end. That final r is usually a light tap, not the strong rolled rr.

Yes, it is natural in Spain.

Cierra bien la cremallera del abrigo antes de salir sounds like a normal everyday instruction, especially from a parent, partner, or friend.

Native speakers might also say things like:

• Abrígate bien antes de salir. = Wrap up warm before going out.
• Súbete bien la cremallera del abrigo antes de salir. = Zip your coat up properly before going out.
• No te dejes la cremallera abierta. = Don’t leave the zipper open.

But the original sentence is absolutely idiomatic and clear.