When and How to use Subjunctive
 

Why do you use subjunctive to refer to a future action dependent on another action? What would be an example of this besides "ir + a + infinitive + another action"? Why wouldn't this use an indicative verb form in future?

When do you use subjunctive? I know it is used to express doubt/feelings/impersonal/wants and refer to unknown things. Is there anything else I'm missing?

The subjunctive is used for/with: emotional reactions, value judgments, doubt, denial, uncertainty, verbs of volition, non-existence, something outside of one's experience, something unidentified, a future event (especially with certain time coordinator phrases, like antes de que).
Other phrases of place or manner trigger the use of the subjunctive: para que, con tal de que, a menos que

Provide specific examples, and we can explain why the subjunctive was used.

I can't come up with examples since I don't understand this part: "refer to a future action dependent on another action". What does that even mean??

Perhaps they meant something like this example:

Cuando llegue, vamos al supermercado.
=When she gets here, we'll go to the supermarket.

You can switch the clauses around to fit your earlier example.
The future 'going to the super' is dependent on a future event that is cast in the subjunctive. The secondary clause is not cast in the subjunctive because it's a future event. It's because there is a sense of uncertainty.

Hope that helps.

:)

A little correction. Again, I think your mind is playing with you. :) Or rather your fingers!...:D

Sorry to disagree, Hernán. I find nothing wrong with "cuando llegue, vamos al supermercado".
Using present tense to talk about a future action in this kind of contexts sounds a lot more natural than using the future tense.

Rusty I have highlighted that word because, you have switched the word arrive for gets, I wanna understand the main phrase because it very weir for me the form in that you wrote the sentence, I have learnt before that get is meaning obtener recibir, but never I didn't learn that get is llegar, therefore I have doubt in the phrase Could you explain me it more minutely for me.:)

Me neither, what I found wrong was the translation of "When she gets here, we'll go to the supermarket."

:)

:owl: (I am looking at you) :lol:

When she gets here = When she arrives

Rusty te lo corrigió correctamente. "To get here" significa venir o llegar aquí dependiendo de como lo estes usando.

"Get" solo significa obtener, recibir etc.

"Get" se ocupa en muchas otras instancias que significan algo diferente.

Si sigues mi consejo de leer una novela en ingles y traducirla al español te vas a dar cuenta de esto que te digo mas rapido. :-)