Mi amiga y yo queremos subir a la torre para ver el valle.

Both are possible, but mi amiga y yo sounds more natural and polite. In Spanish, as in English, speakers often put themselves last in a list.

So mi amiga y yo is the usual equivalent of my friend and I.

No. Mi does not change for gender.

• mi amigo = my male friend
• mi amiga = my female friend

It only changes for number:

• mi = my, singular
• mis = my, plural

So mi amiga is correct because amiga is singular and feminine.

Because the speaker is talking about a female friend. Spanish nouns and many person words show gender, so:

• amigo = male friend / friend in a masculine form
• amiga = female friend

If the friend were male, the sentence would start Mi amigo y yo...

Because the subject is mi amiga y yo, which means my friend and I = we.

The verb querer has to match that subject:

• yo quiero = I want
• tú quieres = you want
• él/ella quiere = he/she wants
• nosotros/nosotras queremos = we want

So mi amiga y yo queremos means my friend and I want.

Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

Here, queremos already tells you the subject is we, so nosotros is unnecessary.

• Mi amiga y yo queremos subir... = perfectly natural
• Nosotros, mi amiga y yo, queremos subir... = possible, but more emphatic or heavy

In normal speech, Spanish usually avoids unnecessary subject pronouns.

After querer, Spanish normally uses another verb in the infinitive, just like English uses to + verb.

• queremos subir = we want to go up / we want to climb
• quiero comer = I want to eat
• quieren salir = they want to leave

So queremos subir literally works like we want to go up.

Because subir often uses a when you are going up to a place.

• subir a la torre = go up to the tower / go up into the tower
• subir al autobús = get on the bus
• subir a la montaña = go up the mountain

Here, a marks the destination.

Two reasons:

1. Torre is a feminine noun, so it takes la, not el.

   • la torre

2. The contraction al only happens with a + el.

   • a + el = al
   • a + la = a la

So:

• al valle would be possible if the noun were masculine with el
• but a la torre is correct because torre is feminine

Because para expresses purpose or goal here: they want to go up the tower in order to see the valley.

• para ver el valle = to see the valley / in order to see the valley

This is a very common structure in Spanish:

• Voy al mercado para comprar fruta. = I’m going to the market to buy fruit.
• Estudia para aprender. = He/She studies to learn.

Por usually expresses other ideas, such as cause, means, exchange, movement through, and so on, so por ver would not fit here.

Because after para, Spanish uses the infinitive when the subject stays the same.

Here, the people who want to go up are also the people who want to see the valley, so Spanish uses:

• para ver = to see

If the subject changed, Spanish would usually use para que + a conjugated verb instead:

• Subimos a la torre para que ella vea el valle.
  = We go up the tower so that she can see the valley.

Spanish often uses the definite article more than English does.

Here, el valle means the valley, probably a specific valley that can be seen from the tower. In context, it sounds natural to use the article.

Spanish commonly uses articles with nouns where English sometimes might not, especially when the thing is identifiable from the situation.

Sometimes, but the meaning changes slightly.

• ver = to see
• mirar = to look at

In this sentence, ver el valle is the most natural choice if the idea is simply to see the valley from the tower.

If you said para mirar el valle, it would sound more like to look at the valley, focusing more on the act of looking.

In most of Spain, ll is pronounced much like the y in yes, so valle sounds roughly like VA-yeh.

A few notes:

• v in Spanish is usually pronounced more like a soft b/v sound, not a strong English v
• ll and y are pronounced the same in most of the Spanish-speaking world

So valle is approximately BA-yeh or VA-yeh, depending on how you hear it through English spelling.