Según el tiempo, podemos ir a la playa o quedarnos en casa.

Yes, tiempo can mean both time and weather in Spanish.

In this sentence, Según el tiempo means depending on the weather or according to the weather, not according to the time. The context makes it clear, because going to the beach or staying at home depends much more naturally on the weather.

A very common pattern is:

• Hace buen tiempo = The weather is good
• Hace mal tiempo = The weather is bad

So here, el tiempo is being used in that same weather sense.

Según usually means according to, depending on, or based on.

In this sentence, Según el tiempo is best understood as:

• Depending on the weather
• According to the weather

It introduces the condition that influences the decision.

Other examples:

• Según el profesor, el examen será fácil. = According to the teacher, the exam will be easy.
• Según cómo me sienta, saldré o me quedaré en casa. = Depending on how I feel, I’ll go out or stay home.

Podemos ir simply means we can go.

Here, ir a la playa means to go to the beach. That is enough on its own.

Irse usually adds the idea of leaving or going away from a place:

• Nos vamos = We’re leaving / We’re going away

So:

• Podemos ir a la playa = We can go to the beach
• Podemos irnos = We can leave

In this sentence, the focus is the destination (a la playa), so ir is the natural choice.

Because the verb here is quedarse, not just quedar.

Quedarse means to stay or to remain:

• quedarnos en casa = to stay at home

The -nos means ourselves / us, so quedarnos is for us to stay.

This happens because after podemos, Spanish uses the infinitive, and reflexive pronouns can be attached to the end of the infinitive:

• podemos quedarnos
• nos podemos quedar

Both are correct.

By contrast, quedar without se often has other meanings, such as:

• to arrange / agree
• to be located
• to remain left over

So in this sentence, quedarnos is the correct form for staying.

Yes. Both are correct:

• podemos quedarnos en casa
• nos podemos quedar en casa

With verbs like poder + infinitive, object or reflexive pronouns can usually go in either place:

1. before the conjugated verb
2. attached to the infinitive

So both versions mean the same thing:

• We can stay at home

The version in your sentence, podemos quedarnos, is very common and natural.

Because o simply joins two infinitives here:

• ir a la playa
• quedarnos en casa

The a belongs to ir a la playa, not to the whole structure.

So the sentence is:

• podemos
  • ir a la playa
• o
  • quedarnos en casa

The second option uses quedarse en casa, and that verb does not need a before it.

En casa is the usual way to say at home or in the house/home in a general sense.

So:

• quedarnos en casa = stay at home

Spanish often uses casa without an article when it means home in the general personal sense.

Compare:

• Estoy en casa. = I’m at home.
• Estoy en la casa de Ana. = I’m in Ana’s house.

So en casa is the natural expression here.

In Spanish, the present tense is often used to talk about current possibilities or near-future plans.

So podemos ir literally means we can go, but depending on context it can also imply:

• we could go
• we can go later / today / this weekend

In this sentence, the idea is that this is an available option right now, depending on the weather.

Spanish does not always need a future tense where English might use one.

Not exactly. Según el tiempo is broader than if the weather is good.

It means something like:

• depending on the weather
• according to the weather

That suggests the weather will help determine which option is best.

So the sentence is closer to:

• Depending on the weather, we can go to the beach or stay at home.

If you said si hace buen tiempo, that would specifically mean:

• if the weather is good

That is a narrower idea than según el tiempo.

O means or.

In this sentence:

• ir a la playa o quedarnos en casa = go to the beach or stay at home

Usually it stays o, but before words beginning with an o sound, it changes to u to avoid repetition of the same sound:

• siete u ocho = seven or eight
• hombres u mujeres = men or women

But here the next word is quedarnos, so it remains o.

Yes, it is understandable and natural, but in everyday conversation many speakers might more often say things like:

• Según haga, podemos ir a la playa o quedarnos en casa.
• Dependiendo del tiempo, podemos ir a la playa o quedarnos en casa.
• Si hace bueno, podemos ir a la playa; si no, nos quedamos en casa.

Your original sentence is still correct. It has a slightly neutral, general feel: depending on the weather.

The sentence breaks down like this:

• Según el tiempo = depending on the weather
• podemos = we can
• ir a la playa = go to the beach
• o = or
• quedarnos en casa = stay at home

So the structure is:

condition/topic + modal verb + option 1 + or + option 2

More abstractly:

• Según X, podemos A o B.

That makes it a useful pattern you can reuse:

• Según el presupuesto, podemos comprar esto o esperar.
• Según la hora, podemos salir ahora o más tarde.