Después de la cena, nos sentamos en el banco de la plaza y miramos el mar.

Because después is normally followed by de before a noun or pronoun.

• después de la cena = after dinner
• después de clase = after class
• después de eso = after that

If a verb follows, Spanish often uses después de + infinitive:

• después de cenar = after having dinner / after dinner

So de is required here.

Spanish uses the definite article much more often than English. With meals, body parts, general concepts, and many other nouns, Spanish often includes el/la/los/las where English does not.

So:

• después de la cena = after dinner
• antes del desayuno = before breakfast

This is completely normal in Spanish and does not sound unusually specific.

Because the verb here is sentarse, which means to sit down. It is a pronominal verb, so it uses a reflexive pronoun:

• me siento
• te sientas
• se sienta
• nos sentamos

So nos sentamos means we sat down.

Without the pronoun, sentamos usually comes from sentar, which often means to seat someone or to settle/place something.

For example:

• Sentamos al niño en la silla = We seated the child on the chair
• Nos sentamos en la silla = We sat down on the chair

In this sentence, they are understood as the preterite, the tense used for completed past actions:

• nos sentamos = we sat down
• miramos = we looked at / watched

However, for nosotros forms of regular -ar verbs, the present and preterite look identical:

• miramos can mean we look or we looked
• nos sentamos can mean we sit down or we sat down, depending on context

Here, the time expression and the whole sentence clearly place it in the past.

Because Spanish usually drops subject pronouns when the verb ending already shows who the subject is.

• nos sentamos
• miramos

Both forms clearly indicate we, so nosotros is unnecessary.

You could say nosotros nos sentamos for emphasis or contrast, but in normal speech it is usually omitted.

With sentarse, Spanish normally uses en to say where someone sits:

• sentarse en una silla = to sit on a chair
• sentarse en el sofá = to sit on the sofa
• sentarse en el banco = to sit on the bench

So en is the normal preposition here, even though English may use on.

No. Here banco means bench.

Spanish banco can mean different things depending on context:

• banco = bank, financial institution
• banco = bench, especially a public bench

Because the sentence says en el banco de la plaza, the meaning is clearly the bench in the square.

In Spain, plaza usually means a public square or town square, often an open central area surrounded by buildings, cafés, shops, or benches.

So el banco de la plaza suggests the bench in that public square.

A plaza is not exactly the same as the English word plaza in the sense of a shopping center. In Spain, it usually refers to an actual square in a town or city.

Both are possible, but they are slightly different.

• el banco de la plaza = the bench of the square / the square’s bench, meaning the bench that belongs to or is located in that square
• el banco en la plaza = the bench in the square, focusing more directly on location

In many cases, Spanish naturally uses de to connect one noun to another this way. So el banco de la plaza sounds very normal.

Because mirar and ver are not exactly the same.

• mirar = to look at, to watch, to direct your eyes toward something
• ver = to see

So:

• miramos el mar = we looked at the sea / we watched the sea
• vimos el mar = we saw the sea

Here the idea is that they were sitting there and intentionally looking at the sea, so miramos fits better.

Again, Spanish often uses the definite article where English does not.

• miramos el mar = we looked at the sea
• escucho la música = I listen to music
• me gusta el café = I like coffee

Using el mar is the normal way to refer to the sea in general or the sea visible in that context.

In standard Peninsular Spanish, the c before e or i, and the z, are usually pronounced like the th in think.

So in much of Spain:

• cena sounds roughly like THAY-na
• plaza sounds roughly like PLA-tha

But the s in sentamos stays an s sound.

This is one of the most noticeable pronunciation differences between most of Spain and most of Latin America, where cena and plaza would usually be pronounced with an s sound instead.