Learn Spanish (Latin America): Al usar la llave, desbloqueas el portal. - Upon using the key, you unlock the portal.

The structure al + infinitive is a special temporal phrase that means "upon doing something" or "when doing something." After al, the verb always stays in its infinitive (dictionary) form.

Since usar is in the infinitive, how do we know who is using the key?

The person doing the action in an al + infinitive phrase is understood from the main clause. Because the main verb is desbloqueas (the informal "you" form), it is clearly understood that "you" are also the one using the key.

Could I just say Cuando usas la llave instead of Al usar la llave?

Yes, Cuando usas la llave is perfectly correct and means essentially the same thing. However, al + infinitive is a very common and concise way to express this timing in Spanish, similar to saying "Upon using" or "By using" in English.

Is desbloqueas related to the English word "block"?

Yes! The base verb is bloquear (to block or to lock). By adding the prefix des-, which reverses an action just like "un-" does in English, you get desbloquear (to unblock or to unlock).