Revisamos el chaleco salvavidas antes del simulacro de seguridad.

Yes. Revisamos is the nosotros form of revisar, and for many -ar verbs, the present and preterite forms are identical in nosotros.

So revisamos can mean either:

• we check / inspect / review
• we checked / inspected / reviewed

You usually know which one is meant from the wider context. On its own, the form is ambiguous.

Because Spanish often omits subject pronouns when the verb already makes the subject clear.

• Revisamos already tells you the subject is we
• so nosotros is not necessary

If you did say Nosotros revisamos..., it would sound more emphatic, as if you were contrasting we with someone else.

Not usually. This is a very common learner question because it can look like a direct match, but in many everyday contexts revisar means:

• to check
• to inspect
• to look over
• to examine

So here revisamos el chaleco salvavidas means we checked/inspected the life jacket, not we revised the life jacket.

Depending on context, revisar can sometimes mean review, but it very often has the idea of checking something carefully.

El means the, so it refers to a specific life jacket, or one that is already understood in the situation.

Spanish often uses the definite article when talking about something known or identifiable in context. For example, on a ship or during training, there may be a particular life jacket being checked.

If you said un chaleco salvavidas, it would mean a life jacket, which sounds less specific.

In chaleco salvavidas, salvavidas works as part of a compound noun/expression, not like a normal adjective that changes form.

So you get:

• el chaleco salvavidas
• los chalecos salvavidas

Notice that chaleco becomes plural, but salvavidas usually stays the same.

This is normal with a number of compound words in Spanish.

Because de + el contracts to del in Spanish.

So:

• de el → del

That means:

• antes del simulacro = before the drill

This contraction is required in normal Spanish.

Because antes normally uses de before a noun or an infinitive.

Examples:

• antes de la clase = before class
• antes de salir = before leaving
• antes del simulacro = before the drill

So in your sentence, antes de + el simulacro becomes antes del simulacro.

Here simulacro means a drill, practice exercise, or mock emergency exercise.

So it is not just a vague simulation in the abstract. In safety contexts, simulacro is the normal word for a drill people carry out to practise procedures.

For example:

• simulacro de incendio = fire drill
• simulacro de evacuación = evacuation drill

So simulacro de seguridad is a safety drill.

Spanish very often uses the pattern noun + de + noun where English prefers either:

• an adjective, or
• a noun used like an adjective

So:

• simulacro de seguridad literally = drill of safety
• natural English = safety drill

This structure is extremely common in Spanish. A few similar examples are:

• cinturón de seguridad = seat belt
• gafas de sol = sunglasses
• plan de emergencia = emergency plan

Yes. Spanish word order is more flexible than English word order.

For example, these are both natural:

• Revisamos el chaleco salvavidas antes del simulacro de seguridad.
• Antes del simulacro de seguridad, revisamos el chaleco salvavidas.

The second version puts more emphasis on the time expression before the safety drill.

So the original order is perfectly normal, but it is not the only possible order.