Cuando baja la marea, abrimos la sombrilla y nos sentamos cerca de la orilla.

Because baja is the present indicative, which fits a habitual or repeated action:

• Cuando baja la marea, abrimos la sombrilla... = When the tide goes out, we open the parasol...

This sounds like something that generally happens whenever that situation occurs.

If you were talking about one future occasion, Spanish would normally use the present subjunctive after cuando:

• Cuando baje la marea, abriremos la sombrilla. = When the tide goes out, we will open the parasol.

So:

• cuando + indicative → habitual / general / repeated
• cuando + subjunctive → future event not yet happened

It most naturally sounds like a routine or repeated situation.

The verbs are in the present tense:

• baja
• abrimos
• nos sentamos

In Spanish, the present tense often describes habitual actions, just like in English:

• When the tide goes out, we open the parasol and sit near the shore.

If you wanted to describe what is happening right now, Spanish would more likely use forms such as:

• está bajando la marea
• estamos abriendo la sombrilla
• nos estamos sentando...

But in this sentence, the simple present sounds more like something we usually do.

Because Spanish often omits subject pronouns when the verb ending already shows who the subject is.

Here:

• abrimos = we open
• nos sentamos = we sit down

The -mos ending already tells you the subject is we, so nosotros is unnecessary unless you want emphasis or contrast.

For example:

• Nosotros abrimos la sombrilla, pero ellos se quedan de pie.

Here nosotros is used because it contrasts with ellos.

Nos is a reflexive pronoun meaning ourselves.

The verb is sentarse, which means to sit down.

So:

• nos sentamos = we sit down / literally we seat ourselves

This is different from sentar, which usually means to seat someone:

• Siento al niño en la silla. = I seat the child in the chair.

But:

• Me siento. = I sit down.
• Te sientas. = You sit down.
• Nos sentamos. = We sit down.

Normally, no, not with this meaning.

• Sentarse = to sit down
• Sentar = to seat someone or to fit/suit someone

So:

• Nos sentamos cerca de la orilla = correct
• Sentamos cerca de la orilla = incomplete or wrong for we sit down

Without nos, sentamos would usually need a direct object:

• Sentamos al niño en la arena. = We seat the child on the sand.

Because cerca is used with the preposition de.

The fixed expression is:

• cerca de = near / close to

So you say:

• cerca de la orilla
• cerca del mar
• cerca de casa

Not:

• cerca la orilla
• cerca el mar

This is just something you need to learn as a set phrase.

They are related, but not the same.

• la playa = the beach
• la orilla = the shore / water’s edge / edge

In this sentence, cerca de la orilla means near the shoreline, close to where the water meets the sand.

So:

• Estamos en la playa. = We are at the beach.
• Estamos en la orilla. = We are at the water’s edge.

Also, orilla can mean edge in other contexts too:

• la orilla del río = the riverbank
• la orilla de la mesa = the edge of the table

Spanish uses definite articles more often than English.

Here, the nouns are treated as specific or understood from context:

• la marea = the tide
• la sombrilla = the parasol
• la orilla = the shore

In English, we might sometimes drop the article in similar expressions, but Spanish often keeps it.

For example:

• sube la marea = the tide comes in
• baja la marea = the tide goes out

Using la here sounds natural and standard.

They are both umbrella-like objects, but they are used for different things:

• sombrilla = parasol / sun umbrella
• paraguas = rain umbrella

In a beach context, sombrilla is the natural word.

Examples:

• Abrimos la sombrilla en la playa. = We open the parasol at the beach.
• Abro el paraguas porque llueve. = I open the umbrella because it’s raining.

So in this sentence, sombrilla is exactly the right word.

Yes. In Spanish, abrir is commonly used for things like umbrellas and parasols.

So:

• abrir la sombrilla = to open / put up the parasol
• abrir el paraguas = to open the umbrella

English often says put up, but Spanish usually says abrir.

You might also hear other expressions in certain contexts, but abrimos la sombrilla is completely natural.

Because the sentence begins with a cuando-clause:

• Cuando baja la marea, ...

When a subordinate clause like this comes before the main clause, Spanish normally uses a comma.

So this is standard:

• Cuando baja la marea, abrimos la sombrilla...

If the order were reversed, the comma would usually disappear:

• Abrimos la sombrilla y nos sentamos cerca de la orilla cuando baja la marea.

Literally, yes, because bajar often means to go down or to lower.

But in natural English, you would usually say:

• the tide goes out
• the tide goes down

So:

• baja la marea = literally the tide goes down
• natural English = the tide goes out

Spanish often uses simple motion/change verbs where English prefers a more idiomatic expression.

That is the normal Spanish word order:

• verb + object
• abrimos la sombrilla = we open the parasol

Then:

• y nos sentamos = and we sit down

Spanish word order is often similar to English in simple statements, but Spanish is generally a bit more flexible. In this sentence, though, the order is completely standard and neutral.

Yes. In this sentence, cuando can feel very close to whenever, because the sentence describes a repeated situation.

So:

• Cuando baja la marea, abrimos la sombrilla...

can be understood as:

• When the tide goes out, we open the parasol...
• Whenever the tide goes out, we open the parasol...

English often makes the habitual meaning clearer with whenever, but Spanish can simply use cuando.