Hoy llevo puesta la bufanda roja porque hace frío.

Spanish often leaves out subject pronouns when they are clear from the verb ending. Here, llevo already tells you the subject is I.

So:

Hoy llevo puesta la bufanda roja... = Today I’m wearing the red scarf...

You could say Yo llevo puesta la bufanda roja, but that would usually add emphasis, contrast, or correction, such as I’m the one wearing it.

Llevar + past participle/adjective is a very common way to talk about what someone has on.

So llevo puesta la bufanda roja means I’m wearing the red scarf or more literally I have the red scarf on.

In this structure:

• llevo = I wear / I am wearing / I have on
• puesta comes from poner and describes the item as put on

Similar examples:

• Llevo puestas las gafas = I’m wearing my glasses
• Lleva puesto un sombrero = He/She is wearing a hat

Because it agrees with la bufanda, which is feminine singular.

Agreement works like this:

• la bufanda → puesta
• el abrigo → puesto
• las botas → puestas
• los guantes → puestos

So the form of puesto/puesta/puestos/puestas changes to match the thing being worn, not the person wearing it.

No. You can also say:

Hoy llevo la bufanda roja porque hace frío.

That is also natural and correct.

Adding puesta makes the idea of wearing it on your body more explicit. It can sound a little more descriptive, as if you are stressing that the scarf is actually on.

So:

• llevo la bufanda roja = I’m wearing the red scarf
• llevo puesta la bufanda roja = I’ve got the red scarf on / I’m wearing the red scarf

For clothing and accessories, llevar is usually the most natural everyday verb in Spanish.

• llevar una bufanda = to wear a scarf
• usar una bufanda = to use/wear a scarf

Usar is possible, but it often sounds more general, more like use, or less idiomatic in ordinary speech about what someone has on. A Spanish speaker will usually prefer llevar for clothes, glasses, jewellery, scarves, and similar items.

In Spanish, colour adjectives normally come after the noun.

So:

• la bufanda roja = normal, standard word order
• la roja bufanda = unusual, literary, poetic, or emphatic

This is why learners should usually place colour words after the noun:

• el coche rojo
• la camisa blanca
• las botas negras

Yes, it can go after.

Both of these are natural:

• Llevo puesta la bufanda roja
• Llevo la bufanda roja puesta

The version in your sentence is very common. Putting puesta after the noun is also fine and may sound slightly more focused on the item itself.

A good rule for learners is: both are correct, and you will hear both.

La means the, so it suggests a specific scarf, probably one that is known in the situation or already identifiable.

• la bufanda roja = the red scarf
• una bufanda roja = a red scarf

Both are grammatically possible, but they do not mean exactly the same thing. The sentence with la sounds like the speaker has a particular red scarf in mind.

Because hace frío is the normal Spanish weather expression for it’s cold.

Here, hacer is used impersonally for weather:

• Hace frío = It’s cold
• Hace calor = It’s hot
• Hace viento = It’s windy

By contrast:

• Está frío usually means something specific is cold, such as La sopa está fría
• Es frío usually means something is cold by nature, character, or general quality, such as Es un país frío or Es una persona fría

So for the weather in general, hace frío is the right expression.

In this sentence, porque means because.

• porque = because
• por qué = why

Examples:

• Llevo la bufanda porque hace frío = I’m wearing the scarf because it’s cold
• ¿Por qué llevas la bufanda? = Why are you wearing the scarf?

This is a very common spelling distinction in Spanish, so it is worth learning early.

Yes. Spanish word order is flexible.

You could say:

• Hoy llevo puesta la bufanda roja porque hace frío
• Llevo puesta la bufanda roja hoy porque hace frío

But putting hoy at the beginning is very natural because it sets the time frame immediately: today.

It can also give a slight contrastive feeling, like today, as opposed to other days.

Yes, but it means something slightly different.

• Llevo puesta la bufanda roja focuses on the current state: I am wearing the red scarf
• Me he puesto la bufanda roja focuses on the action: I have put on the red scarf

So:

• llevo puesta = what I have on now
• me he puesto = the act of putting it on

In many situations, both are possible, but they are not identical.

Because roja agrees with bufanda, just like puesta does.

Since bufanda is feminine singular, the adjective must also be feminine singular:

• la bufanda roja
• el abrigo rojo
• las bufandas rojas
• los abrigos rojos

This agreement is one of the main things English speakers have to get used to in Spanish: adjectives often change form to match the noun.