Nos encordamos junto al compañero de cordada.

Because the verb here is encordarse, a pronominal verb. In climbing, encordarse means to rope oneself up / to tie in.

So nos encordamos means something like we roped ourselves up or we tied in.

Without nos, encordamos would come from encordar, which is normally understood more as to rope something/someone rather than to rope ourselves up.

In practice, it suggests a shared action involving the group, and in this climbing context it is best understood as we tied in / we roped up together.

The pronoun nos can sometimes feel reflexive (ourselves) and sometimes reciprocal (each other), but here the important point is that Spanish uses the pronominal verb encordarse for this action. A learner does not need to force a perfect one-word English equivalent for nos every time.

It can be either:

• present: we rope up / we tie in
• preterite: we roped up / we tied in

For -ar verbs, the nosotros form is identical in the present and the preterite: encordamos.

So only the wider context tells you which one it is.

For example:

• Antes de subir, nos encordamos. = could mean Before we climb, we rope up.
• Ayer nos encordamos temprano. = clearly Yesterday we roped up early.

Junto a usually means next to, beside, or together with / alongside, depending on context.

In this sentence it gives the idea of being with / next to the climbing partner while roping up.

It is a common Spanish expression:

• junto a la puerta = next to the door
• junto a sus amigos = together with / alongside his friends

So here it adds a sense of proximity or being side by side.

Because a + el contracts to al in standard Spanish.

So:

• junto a + el compañero
  becomes
• junto al compañero

This contraction is basically obligatory unless El is part of a proper name.

Yes, and in many situations con may actually sound more direct and natural if you want to emphasize who you roped up with.

The difference is roughly this:

• encordarse con alguien = to rope up with someone
• encordarse junto a alguien = to rope up next to / alongside someone

So con focuses more on the partner as the person you are tied in with, while junto a adds a spatial idea of being beside that person.

It is a climbing expression. Cordada refers to a rope team or the group of climbers linked on a rope. So compañero de cordada means your rope partner or climbing partner.

This is more specific than just compañero, because it identifies the person by their role in the climb.

Because compañero de cordada works as a fairly fixed expression meaning rope partner.

In Spanish, when de + noun describes a person’s type, role, or function, the article is often omitted:

• profesor de español
• zapatos de montaña
• compañero de cordada

If you said de la cordada, that would sound more like of the rope team, referring to a specific team already identified in the conversation.

So:

• compañero de cordada = a rope partner / climbing partner
• compañero de la cordada = the partner from that particular rope team

Spanish often uses the definite article where English might prefer a possessive, especially when the person is already clear from context.

So el compañero de cordada can naturally mean the climbing partner, understood as our/the relevant one in this situation.

Spanish does this a lot when the reference is obvious. It does not always need mi, tu, nuestro, etc.

Mostly, yes. It is a fairly specialized verb connected with ropes, especially in climbing, mountaineering, and similar contexts.

So this is not the kind of verb you will hear all the time in everyday conversation unless the topic is outdoor sports, rescue work, or something similar.

Yes. Spanish word order is fairly flexible, especially with prepositional phrases like junto al compañero de cordada.

For example, you could also say:

• Junto al compañero de cordada, nos encordamos.

But the original order is more neutral and natural in most contexts:

• Nos encordamos junto al compañero de cordada.

The main information stays the same; the change is mostly about emphasis or style.