Cuando terminemos de podar esa rama, abriremos la ventana para que entre más luz.

Because cuando often triggers the subjunctive when it refers to a future action that has not happened yet.

Here, cuando terminemos de podar esa rama means when we finish pruning that branch. Since the finishing is still in the future, Spanish uses the present subjunctive: terminemos.

Compare:

• Cuando terminamos de podar, abrimos la ventana.
  = When we finished pruning / when we finish pruning as a habitual or past-like fact, depending on context
• Cuando terminemos de podar, abriremos la ventana.
  = When we finish pruning, we’ll open the window

So in future time clauses, Spanish often uses:

• cuando + present subjunctive

even though English uses the present:

• when we finish

Because it describes what will happen next.

The sentence sets up a sequence:

1. first, we finish pruning
2. then, we will open the window

So abriremos is the simple future of abrir.

You could also hear other natural options in Spanish, depending on style and context:

• abriremos la ventana = we will open the window
• vamos a abrir la ventana = we’re going to open the window
• abrimos la ventana = we open / we’ll open the window, with present used for near future in conversation

But abriremos is perfectly natural and clear.

Because terminar is commonly followed by de + infinitive when it means to finish doing something.

So:

• terminar de podar = to finish pruning
• terminar de comer = to finish eating
• terminar de hablar = to finish speaking

So cuando terminemos de podar esa rama literally means when we finish pruning that branch.

Without de, the sentence would sound wrong here.

Podar means to prune or to trim, especially with plants, trees, bushes, or branches.

So podar esa rama means:

• to prune that branch
• to trim that branch
• sometimes even to cut back that branch, depending on context

It is more specific than a general verb like cortar (to cut).
Podar suggests garden or plant maintenance.

These are Spanish demonstratives, and they show distance or perspective.

• esta rama = this branch
• esa rama = that branch
• aquella rama = that branch over there / that far-off branch

In Spain Spanish, the basic contrast is often:

• esta: near the speaker
• esa: near the listener or already identified in the conversation
• aquella: farther away from both

So esa rama usually means that branch, one that is not right here with the speaker, or one both people already know which one it is.

Because para que is followed by the subjunctive when it introduces a purpose clause.

Here the purpose is:

• we will open the window
• so that more light can come in

So:

• para que entre más luz = so that more light comes in / can come in

The verb entre is the present subjunctive of entrar.

This is a very common pattern:

• Cierra la puerta para que no entre frío.
  = Close the door so that cold air doesn’t come in.
• Enciende la lámpara para que veamos mejor.
  = Turn on the lamp so that we can see better.

Because para + infinitive is usually used when the subject is the same in both parts.

For example:

• Abrimos la ventana para ventilar la habitación.
  = We open the window to air out the room.

Here, we open the window, and we air out the room.

But in your sentence, the second action is not something we do directly. The subject changes:

• we open the window
• more light enters

Because the subject changes, Spanish uses:

• para que + subjunctive

So:

• para que entre más luz = correct

The subject is más luz.

So the structure is:

• para que entre más luz

Literally:

• so that more light enters

Even though English often says so that more light comes in or to let in more light, Spanish uses the verb entrar very naturally with luz.

So la luz entra = the light comes in / enters.

Because más luz means more light in a general, uncountable sense.

In English, we also usually say:

• more light not
• the more light

Spanish works similarly here:

• más luz = more light
• mucha luz = a lot of light
• poca luz = little light

You would only use an article if the context specifically called for one, but in this sentence the general quantity is what matters.

Yes, it is appropriate here.

The first part, Cuando terminemos de podar esa rama, is an introductory subordinate clause. In Spanish, when this kind of clause comes first, it is normally separated from the main clause by a comma:

• Cuando terminemos de podar esa rama, abriremos la ventana...

If the order is reversed, the comma is usually not needed:

• Abriremos la ventana para que entre más luz cuando terminemos de podar esa rama.

So the comma helps mark the break between the when-clause and the main statement.

Yes, literally that is exactly what it means.

• entre = enters / comes in
• más luz = more light

So the literal sense is:

• so that more light enters

But in natural English, you would more often say:

• so that more light comes in
• to let in more light

So the Spanish is literal and idiomatic at the same time.

In standard Peninsular Spanish, a few things stand out:

• cu in cuando sounds like kw
• z in podar esa rama, abriremos la ventana para que entre más luz does not appear, but the c before e in hacer-type words would sound like the th in thin; here there is no such c, but there is z in luz, which in Spain is usually pronounced like th in thin
• So luz sounds roughly like looth
• v and b are pronounced very similarly in Spanish, so abriremos does not have an English v sound

A rough guide:

• Cuando terminemos de podar esa rama, abriremos la ventana para que entre más luz.
• roughly: KWAN-do ter-mee-NAY-mos de po-DAR EH-sa RA-ma, a-bree-REE-mos la ben-TA-na PA-ra ke EN-tre mas LOOTH

That is only an approximation, but it highlights the main Spain pronunciation feature in luz.