Después de que te vistas, desayunaremos en la terraza si hace sol.

Because después de que normally takes the subjunctive when it refers to something that has not happened yet.

Here, the getting dressed is still in the future relative to the breakfast, so Spanish uses:

• después de que te vistas

Not:

• después de que te vistes

Te vistas is the present subjunctive of vestirse.

A useful contrast:

• Después de que te vistas, desayunaremos... = future/expected action
• Después de que te vestiste, desayunamos... = past completed action

It comes from vestirse, which means to get dressed.

The te is the reflexive pronoun for tú. It shows that the action is done to oneself:

• me visto = I get dressed
• te vistes = you get dressed
• se viste = he/she gets dressed

So te vistas means that you get dressed in the subjunctive.

Because vestir is a stem-changing verb.

Its stem changes from e to i in these forms:

• visto
• vistes
• vista
• vistas
• vistan

So the subjunctive comes from the yo form visto, which gives:

• vista
• vistas
• vista
• vistamos
• vistáis
• vistan

That is why you get te vistas.

Because the sentence is talking about something that will happen later, so the future is a very natural choice.

• desayunaremos = we will have breakfast

Spanish also sometimes uses the present tense for planned future events, especially in conversation:

• Después de que te vistas, desayunamos...

That can sound more immediate or conversational. But desayunaremos is clear, standard, and explicit.

After si meaning if, Spanish normally uses the indicative for real or possible conditions.

So you say:

• si hace sol

not

• si haga sol

The subjunctive is generally not used after this kind of si.

A very common pattern is:

• Si + present indicative, future
• Si hace sol, desayunaremos...

Because after si for a normal future condition, Spanish uses the present indicative, not the future.

So Spanish says:

• si hace sol = if it is sunny / if the sun is out

not:

• si hará sol

This is one of those patterns that differs from what an English speaker might expect.

It is a standard Spanish weather expression.

Spanish often uses hacer with weather nouns:

• hace frío = it is cold
• hace calor = it is hot
• hace viento = it is windy
• hace sol = it is sunny / the sun is out

English uses it is, but Spanish often uses hace in these expressions. It is just the normal idiomatic way to say it.

Because Spanish often leaves subject pronouns out when the verb form already makes the subject clear.

Here:

• te vistas already points to tú
• desayunaremos clearly means we

So tú and nosotros are unnecessary unless you want emphasis or contrast:

• Después de que tú te vistas, nosotros desayunaremos...

That sounds more emphatic, not more natural by default.

Because en marks location, while a usually marks movement toward a destination.

• desayunaremos en la terraza = we will have breakfast on the terrace
• vamos a la terraza = we are going to the terrace

So here the idea is where the breakfast happens, not movement to that place.

Not naturally in this sentence.

Después de + infinitive is most natural when the subject is the same as the subject of the main clause:

• Después de vestirme, desayunaré.
• After getting dressed, I will have breakfast.

But in your sentence, the person getting dressed is you, while the people having breakfast are we. Because the subjects are different, Spanish normally uses:

• después de que te vistas

That is the right structure here.

It is standard and very natural to use a comma when the sentence begins with a subordinate clause like this:

• Después de que te vistas, desayunaremos...

The comma helps separate the introductory time clause from the main clause.

If the order changes, the comma may disappear:

• Desayunaremos en la terraza si hace sol.

So the comma here is not random; it reflects the structure of the sentence.

Yes, Spanish word order is fairly flexible, as long as the grammar stays correct.

For example:

• Si hace sol, desayunaremos en la terraza después de que te vistas.
• Desayunaremos en la terraza si hace sol, después de que te vistas.

The meaning stays very similar, but the emphasis changes slightly depending on what comes first.

The original sentence is very natural because it presents the sequence clearly: first getting dressed, then breakfast, with the weather condition added at the end.

In standard Spanish, especially as a learner aiming for Spain Spanish, después de que is the safest and most standard choice.

You may sometimes see or hear después que in some regions or varieties, but después de que is the form you should normally use.

So for Spain-focused Spanish, después de que is the best default.

In most of Spain, the z in terraza is pronounced like the th in think.

So it sounds roughly like:

• te-RRA-tha

A few notes:

• the rr is a rolled or trilled r
• the stress falls on ra
• the final z is the Spain pronunciation, not an s sound

In much of Latin America, it would sound more like te-RRA-sa, but for Spain Spanish, th is the expected pronunciation.