Usamos magnesio en la zona de búlder.

Usamos is the first person plural form of usar, so it means we use here.

In this sentence, it is most naturally understood as the present tense:
Usamos magnesio... = We use chalk/magnesium...

A useful extra point: for regular -ar verbs, the nosotros form in the present and the preterite can look the same:

• usamos = we use
• usamos = we used

The context tells you which meaning is intended. In this sentence, the present meaning is the normal one.

Spanish often omits subject pronouns because the verb ending already tells you who the subject is.

• usamos already means we use
• so nosotros usamos is possible, but usually unnecessary

You would only add nosotros if you wanted extra emphasis or contrast, for example:

• Nosotros usamos magnesio, pero ellos no.
  We use chalk, but they don’t.

So the sentence sounds natural without nosotros.

Because magnesio is being used as a mass noun here, in a general sense.

Spanish often leaves out the article with materials or substances when talking about using or needing them in general:

• Usamos agua.
• Necesito harina.
• Compramos magnesio.

So usamos magnesio is like saying we use chalk or we use magnesium carbonate, not we use the chalk.

If you were talking about a specific chalk, you might use an article:

• Usamos el magnesio que compraste ayer.
  We use the chalk you bought yesterday.

In climbing contexts, magnesio usually means climbing chalk.

More literally, it refers to magnesium carbonate, the white powder climbers use on their hands for grip. So even though the word looks like magnesium, the practical meaning in this sentence is closer to:

• chalk
• climbing chalk

This is a good example of where the most natural English translation is not always the most literal one.

It means in the bouldering area or in the bouldering section.

Breakdown:

• en = in / at
• la zona = the area / the zone
• de búlder = for bouldering / of bouldering

So the whole phrase refers to the part of a climbing gym or climbing space used for bouldering.

Spanish often links nouns with de where English prefers a noun used like an adjective.

So:

• zona de búlder = literally zone/area of bouldering
• natural English: bouldering area

This is a very common Spanish pattern:

• zapatos de montaña = mountain shoes / hiking boots
• mesa de madera = wooden table
• sala de espera = waiting room

So de does not always mean just of in a strict sense; often it is simply the normal way Spanish connects two nouns.

Búlder is a Spanish adaptation of the English word boulder, used in climbing to mean bouldering or sometimes a boulder problem area, depending on context.

The accent mark in búlder shows that the stress falls on the first syllable:

• BÚL-der

Without the accent, Spanish spelling rules would suggest a different stress pattern.

In Spain, climbers may use búlder quite commonly, especially in gyms. You may also come across other expressions depending on region or formality.

Because en is the normal Spanish preposition for being in or at a place.

• en la zona de búlder = in the bouldering area
• en el gimnasio = in/at the gym
• en casa = at home

English sometimes chooses between in and at, but Spanish often just uses en for both ideas.

Yes, grammatically it could, because usamos can be either:

• present: we use
• preterite: we used

But without any extra context, most learners should understand this sentence as present tense.

If the speaker clearly wanted the past meaning, the surrounding context would usually make that obvious, for example:

• Ayer usamos magnesio en la zona de búlder.
  Yesterday we used chalk in the bouldering area.

So the form is ambiguous by itself, but the intended meaning normally becomes clear from context.

Most often, yes. It commonly refers to the bouldering area in a climbing gym or indoor climbing wall.

However, it could also be used more generally for any area set aside for bouldering. The exact meaning depends on context.

In everyday climbing Spanish in Spain, this kind of wording is very natural if someone is talking about rules, habits, or equipment in a climbing facility.