La combinación abre el candado de combinación.

They are doing two different jobs:

• La combinación = the combination, the number/code itself
• candado de combinación = combination padlock or combination lock

So even though the same noun appears twice, the first one is the thing that opens the lock, and the second one is part of the name of the object.

This kind of repetition is normal in Spanish when the same word is needed in two different parts of the sentence.

Literally, it means padlock of combination.

In Spanish, de + noun is very commonly used where English often uses one noun to modify another:

• candado de combinación = combination padlock
• cepillo de dientes = toothbrush
• mesa de madera = wooden table

So de combinación describes the type of candado.

Because the nouns have different grammatical genders:

• candado is masculine, so it takes el
• combinación is feminine, so it takes la

This has nothing to do with real-world sex or biology. It is just grammatical gender, which Spanish nouns have.

Also, many nouns ending in -ción are feminine:

• la combinación
• la canción
• la lección
• la información

Abrir is a direct-transitive verb here: something opens something.

So the structure is:

• La combinación = subject
• abre = verb
• el candado de combinación = direct object

Spanish does not need an extra word like with or using in this sentence if the meaning is simply The combination opens the combination lock.

If you wanted to make the idea of using more explicit, you could say something like:

• Con la combinación se abre el candado.
  = With the combination, the lock opens / The lock is opened with the combination.

But the original sentence is grammatically fine.

Literally, abre means opens.

In context, English might naturally say unlocks, because a combination is what lets you unlock a lock. Spanish often still uses abrir for locks, doors, windows, boxes, etc.

So in this sentence, abre can be understood as:

• opens
• or, more naturally in context, unlocks

The exact best English translation depends on context, but the Spanish verb is still abrir.

Yes, grammatically it is fine, though depending on context it may sound a little textbook-like or explanatory.

Spanish does allow inanimate things to be subjects:

• La llave abre la puerta. = The key opens the door.
• Este botón abre el archivo. = This button opens the file.
• La combinación abre el candado. = The combination opens the lock.

A speaker might also phrase it differently in everyday speech, for example:

• La combinación sirve para abrir el candado.
  = The combination is used to open the lock.
• Con la combinación se abre el candado.
  = The lock is opened with the combination.

But the original is still correct.

Because el candado de combinación is a thing, not a person.

The personal a is generally used before a specific human direct object, and sometimes pets or personified beings:

• Veo a María.
• Conozco a tu profesor.

But with objects, you usually do not use it:

• Abro la puerta.
• Cierro la ventana.
• La combinación abre el candado.

So abre el candado is exactly what we expect.

Yes, candado con combinación is possible and understandable, and in some contexts it may sound very natural.

The difference is subtle:

• candado de combinación = a lock whose type is a combination lock
• candado con combinación = a lock that has a combination

In practice, both can work, but de combinación often sounds more like the standard label/name of the object.

Because Spanish usually does not stack nouns together the way English does.

English can say:

• combination lock
• car door
• school bus

Spanish usually connects these ideas with a preposition, especially de:

• candado de combinación
• puerta del coche / puerta del carro
• autobús escolar or another equivalent expression

So de combinación is a very normal Spanish way to express what English packs into a noun modifier.

Candado most commonly means padlock.

If you want to talk about a lock more generally, especially the lock mechanism in a door, Spanish often uses:

• cerradura = lock, lock mechanism
• candado = padlock

So candado de combinación specifically suggests a padlock-type object with a combination.

Yes, somewhat. The original order is straightforward and neutral:

• La combinación abre el candado de combinación.

But Spanish can reorder parts for emphasis or style. For example:

• El candado de combinación lo abre la combinación.
  This is grammatical, but it sounds more marked or contrastive.

Still, the basic subject + verb + object order is the clearest and most natural for learners, and it is what you have here.