Let's look at what al means. Of course we have one al that results from the article el with the preposition a (a + el = al) but that's not what we're referring to today.
We're talking about the al that we you find in sentences like "al ver a mi hermano, me alegré mucho", very useful and makes our Spanish sound more advanced.
One of the meanings is related to time and it can be translated as "when" or "upon" doing something. The verb after is going to always be an infinitive.
An example could be the sentence I mentioned at the beginning:
Al ver a mi hermano, me alegré mucho - When I saw my brother, I got very happy.
You can see that the verb being in infinitive, you choose in which tense to translate it, depending of course on other half of the sentence, that usually goes second: Me alegré mucho is preterite, so I would translate ver in the same past tense.
I also know that the person is "I", like in me alegré mucho, so I can put together "I saw".
Al descubrir la verdad, estábamaos en shock -When discovering the truth, we were in shock.
Al dormir, roncas - When sleeping/ when you sleep, you snore.
Me despedí al irme - I said goodbye when I left
When we have a reflexive or pronominal pronoun, that part does have to agree with the person even though is on an infinitive:
Al levantarse, ella está de mal humor - When getting up / when she gets up, she's in a bad mood.
Al preocuparte, te estresas - When worrying/ when you worry, you stress.
When we translate al as "when", sometimes it can turn more into a cause than just expressing timing, and we can translate it as "since" or "because".
Still, using the verb in infinitive form and looking at the other part of the sentence to know the tense and person of the action:
Al protestar, conseguimos mejores condiciones - Since/because we protested, we got better conditions.
Al salir de noche el sábado, el domingo estaba cansada - Because I went out on Saturday, on Sunday I was tired.
Al morir su madre, no salía de casa - Since/because she mother died, she didn't get out of the house.
This one could be a "when" too: When her mother died, she didn't get out of the house. We would need further context to know which one is more accurate, perhaps both are!
Using "al" in these situations means having another word for when we'd say cuando (when) or como (because/since). You can check here why we would use como instead of porque. This makes for a speech that sounds more polished and complex, of course, and it avoids repetition if we need to use those words more than twice or very close together, specially in writing.
Decide which meaning "al" has in these sentences: time (when/upon) or cause (because) or maybe both are possible:
- Al escuchar la música, recordó su infancia
- Al recibir la herencia, pudo pagar su hipoteca
- Estaba en pánico al entrar al escenario
- Al no tener suficiente agua, la planta se murió
- Te contaré todo al salir de la entrevista
- Al moverse, el tren hizo mucho ruido
Hope I helped and you consider adding these to your vocabulary!
¡Hasta la próxima! :)