Cuando llego a casa, necesito desvestirme y ponerme ropa cómoda para descansar.

Because this sentence describes a habitual action or general routine: When I get home, I need to...

In Spanish, when you talk about things that usually happen, the present tense is very common:

• Cuando llego a casa, ... = When I get home, ...

It does not mean only right now. It can mean whenever this happens or every time this happens.

If it were a one-time future event, Spanish might use a different structure, for example:

• Cuando llegue a casa, ... = When I get home / When I arrive home in the future

So here, llego sounds like a routine.

Because with verbs like llegar, Spanish normally uses a to show destination:

• llegar a casa
• llegar al trabajo
• llegar a Madrid

So:

• llego a casa = I arrive home / I get home

Using en here would be unnatural.

In Spanish, casa often appears without an article when it means home in a general, personal sense.

So:

• llegar a casa = to get home
• estar en casa = to be at home
• volver a casa = to go back home

But la casa is used when you mean the house/building itself more specifically:

• Llegué a la casa de Ana = I arrived at Ana’s house

So in your sentence, a casa means home, not specifically the house as a building.

Because Cuando llego a casa is an introductory time clause.

Spanish often places a comma after an introductory clause, just like English often does:

• Cuando llego a casa, necesito desvestirme...

It helps separate:

1. the time/context part: Cuando llego a casa
2. the main statement: necesito desvestirme...

You may sometimes see variation in informal writing, but the comma is very normal and clear here.

Because necesitar can be followed directly by another verb in the infinitive, just like English need to + verb.

• Necesito desvestirme = I need to get undressed
• Necesito descansar = I need to rest

This is a very common pattern:

• Necesito estudiar
• Necesitamos salir
• Necesitan comer

So necesito + infinitive is completely standard.

Desvestirme is made of:

• des- = a prefix that can suggest reversal or removal
• vestir = to dress
• me = myself

So literally it is something like:

• desvestir-me = to undress myself

In natural English, we usually just say to get undressed or to take my clothes off.

This is a reflexive infinitive, because the action happens to the same person who does it.

Because both verbs are in the infinitive, and in Spanish object/reflexive pronouns are often attached to infinitives:

• desvestirme
• ponerme

This is a very common pattern:

• quiero ducharme
• voy a sentarme
• prefiero acostarme temprano

So in your sentence:

• desvestirme = to undress myself
• ponerme ropa cómoda = to put on comfortable clothes

Because each verb needs its own reflexive pronoun.

You are doing both actions to yourself:

• desvestirme = to undress myself
• ponerme ropa cómoda = to put comfortable clothes on myself

Spanish does not usually use one me for both verbs here. Each reflexive verb keeps its own pronoun.

That is why the sentence says:

• desvestirme y ponerme...

not just:

• desvestirme y poner...

Because ponerse ropa is the usual way to say to put on clothes.

• ponerme ropa cómoda = to put on comfortable clothes

By contrast, vestirse usually means to get dressed in a more general sense:

• Me visto rápido = I get dressed quickly

So both verbs relate to clothing, but they are used a bit differently:

• vestirse = to get dressed
• ponerse + clothing item / ropa = to put on a specific thing or type of clothes

That is why ponerme ropa cómoda sounds very natural here.

In Spanish, ropa is usually a singular collective noun, even though in English clothes is plural.

So Spanish says:

• ropa cómoda = comfortable clothing / comfortable clothes

Not:

• ropas cómodas in this context

And the adjective agrees with ropa, which is:

• feminine
• singular

So:

• ropa cómoda

Just like:

• ropa limpia
• ropa nueva
• ropa informal

Because it agrees with ropa, and ropa is a feminine singular noun.

Agreement in Spanish means the adjective matches the noun in gender and number:

• ropa cómoda
• camisa cómoda
• pantalones cómodos

So here:

• ropa = feminine singular
• cómoda = feminine singular form of cómodo

It expresses purpose: in order to rest or so I can rest.

So:

• necesito desvestirme y ponerme ropa cómoda para descansar

means:

• I need to get undressed and put on comfortable clothes in order to rest

Para + infinitive is a very common way to say in order to:

• Estudio para aprender = I study in order to learn
• Salgo temprano para llegar a tiempo = I leave early to arrive on time

Yes. Both are possible, but they are slightly different in feel.

• desvestirme = to get undressed
• quitarme la ropa = to take my clothes off

Desvestirme is a bit more compact and directly means undress myself.

Quitarme la ropa focuses more literally on removing the clothes.

Both are natural, for example:

• Necesito desvestirme
• Necesito quitarme la ropa

In everyday speech, many speakers use either depending on context.

Yes, but you usually do not need to.

Spanish often omits subject pronouns because the verb ending already shows the subject:

• llego = I arrive
• necesito = I need

So the natural version is:

• Cuando llego a casa, necesito...

You could say:

• Cuando yo llego a casa, necesito...

but that would usually add emphasis, contrast, or a special tone. In neutral Spanish, leaving out yo is more normal.

It sounds most naturally like a routine or repeated situation.

• Cuando llego a casa, necesito...
  = When I get home, I need... / Whenever I get home, I need...

So a native speaker would usually understand it as something that regularly happens.

If you wanted to make it clearly about one future moment, Spanish would more likely say:

• Cuando llegue a casa, necesitaré...
• or Cuando llegue a casa, voy a necesitar...

But your original sentence sounds like a general personal habit.