Por la noche me pongo el pijama y, después de descalzarme, bostezo en el sofá.

Yes. Por la noche is a very common way to say at night / in the evening at night-time, depending on context.

In this sentence, Por la noche means something like At night or In the evening/night-time.

A few useful comparisons:

• por la mañana = in the morning
• por la tarde = in the afternoon / evening
• por la noche = at night

You may also see de noche, but that often feels more like at night / when it is dark in a general sense. Here, por la noche is the natural choice for a routine: At night, I put on my pyjamas...

Because the verb here is ponerse, which means to put on oneself when talking about clothes.

• poner = to put, place
• ponerse = to put on

So:

• Pongo el libro en la mesa = I put the book on the table
• Me pongo el pijama = I put on my pyjamas

The me shows that the action is being done to yourself.

In Spanish, with clothing, body parts, and personal items closely connected to the person, it is very common to use the definite article instead of a possessive.

So Spanish often says:

• me pongo el pijama
• literally: I put the pyjamas on myself

Even though English prefers my pyjamas, Spanish does not need mi here, because it is already obvious whose pyjamas they are from me.

This pattern is extremely common:

• me lavo las manos = I wash my hands
• se quitó los zapatos = he/she took off his/her shoes
• me pongo el abrigo = I put on my coat

Good question. Although many nouns ending in -a are feminine, pijama is masculine:

• el pijama

This is just something you have to learn with the noun. Spanish has a number of masculine nouns ending in -a, such as:

• el problema
• el sistema
• el mapa
• el día

So the ending helps often, but it is not a guaranteed rule.

Because after después de, Spanish normally uses an infinitive when the subject is the same.

Here, the same person does both actions:

1. me pongo el pijama
2. descalzarme
3. bostezo

So Spanish uses:

• después de + infinitive
• después de descalzarme = after taking off my shoes

This is very common:

• Después de cenar, me acuesto = After eating dinner, I go to bed
• Después de lavarme los dientes, duermo = After brushing my teeth, I sleep

If the subject changes, Spanish usually uses a different structure, for example después de que...

Descalzarse means to take off one’s shoes or to become barefoot.

In this sentence, it means:

• descalzarme = taking off my shoes

It is reflexive because the action affects yourself. You are removing your own shoes.

A very common alternative is:

• quitarme los zapatos = to take off my shoes

Both are correct, but descalzarse is a neat, compact verb for this idea.

Because descalzarme is an infinitive, and reflexive pronouns can attach to the end of infinitives.

Compare:

• me pongo = finite verb, pronoun goes before it
• descalzarme = infinitive, pronoun attaches to the end

This is a general rule:

• me levanto = I get up
• quiero levantarme = I want to get up

So después de descalzarme is completely normal Spanish.

It comes from the verb bostezar, which means to yawn.

Here, bostezo is the yo form in the present tense:

• yo bostezo = I yawn

So the sentence is using the present tense to describe a habitual action or routine:

• Por la noche... bostezo en el sofá = At night... I yawn on the sofa

Spanish often uses the simple present for routines, just like English does:

• I brush my teeth and go to bed
• Me lavo los dientes y me acuesto

Because Spanish en often covers both in and on, depending on context.

With furniture and many locations, Spanish naturally uses en where English uses on:

• en el sofá = on the sofa
• en la cama = in bed / on the bed
• en la silla = on the chair

Using sobre here would sound unnatural. Sobre is more like on top of in a more physical or literal sense, and it is not the normal choice for sitting or lying on furniture.

The commas mark that phrase as an inserted time/action phrase between the two main parts of the sentence:

• me pongo el pijama
• bostezo en el sofá

So the middle part, después de descalzarme, is additional information about when the second action happens.

Without the commas, the sentence would still be understandable, but with them it reads more naturally and clearly as a parenthetical element:

• Por la noche me pongo el pijama y, después de descalzarme, bostezo en el sofá.

Yes. Spanish uses the present tense very often for habits and routines.

So this sentence does not mean only I am doing this right now. It can also mean:

• This is what I do at night
• At night, I put on my pyjamas and, after taking off my shoes, I yawn on the sofa

This works just like English:

• At night I put on my pyjamas and yawn on the sofa

Yes, absolutely. In fact, quitarse los zapatos is probably more transparent for many learners and very common in everyday speech.

So you could say:

• Por la noche me pongo el pijama y, después de quitarme los zapatos, bostezo en el sofá.

That means almost the same thing as the original.

The original with descalzarme is perfectly correct; it is just a more specific verb meaning to take off one’s shoes / go barefoot.

Yes, because the sentence is linking two main actions:

• me pongo el pijama
• bostezo en el sofá

The y means and and joins those two parts.

The phrase después de descalzarme is inserted between them, but the basic structure is still:

• me pongo el pijama y bostezo en el sofá

Then the extra phrase tells you the sequence more precisely:

• and, after taking off my shoes, I yawn on the sofa