El mueble de segunda mano incluye madera maciza.

In Spanish, mueble is a masculine noun, so it takes el in the singular: el mueble.

Unlike nouns ending in -o or -a, nouns ending in -e do not give a strong clue about gender, so you usually have to learn the gender with the word:

• el mueble = the piece of furniture
• la fuente = the fountain / source

A good habit is to learn nouns together with their article.

Here, mueble means a piece of furniture or an item of furniture, not furniture in general.

So:

• el mueble = the piece of furniture
• los muebles = the furniture / the pieces of furniture

This is slightly different from English, where furniture is usually uncountable. In Spanish, mueble is a normal countable noun.

Literally, de segunda mano means of second hand. It is the standard Spanish expression for second-hand or used when talking about things that were owned before.

So:

• un coche de segunda mano = a second-hand car
• ropa de segunda mano = second-hand clothes
• un mueble de segunda mano = a second-hand piece of furniture

Even though the literal wording sounds a bit unusual in English, it is a very common fixed expression in Spanish.

Yes, often you can, but the nuance is a little different.

• de segunda mano specifically means second-hand / pre-owned
• usado means used, which can sometimes sound broader

For this sentence:

• El mueble de segunda mano... sounds very natural if you want to stress that it is pre-owned.
• El mueble usado... is possible, but it may sound a bit less idiomatic in some contexts, especially in ads or product descriptions.

In Spain, de segunda mano is extremely common.

Because the subject is singular: El mueble de segunda mano.

The main noun is mueble, which is singular, so the verb must also be singular:

• El mueble ... incluye = The piece of furniture includes...
• Los muebles ... incluyen = The pieces of furniture include...

Even though the subject has several words, the core noun is still just mueble.

Incluye is the third person singular present tense of incluir.

Conjugation:

• yo incluyo
• tú incluyes
• él / ella / usted incluye
• nosotros incluimos
• vosotros incluís
• ellos / ellas / ustedes incluyen

So incluye here means includes.

In Spanish, after verbs like incluir, tener, llevar, or usar, a material or substance often appears without an article when speaking in a general sense.

So:

• incluye madera maciza = it includes solid wood
• tiene acero inoxidable = it has stainless steel
• usa algodón orgánico = it uses organic cotton

If you said incluye la madera maciza, it would usually sound more specific, as if you were referring to a particular solid wood already identified in the conversation.

Madera maciza means solid wood.

It refers to real wood all the way through, rather than engineered wood, chipboard, veneer, or similar materials.

This is a very common phrase in product descriptions, especially for furniture:

• mesa de madera maciza = solid wood table
• puerta de madera maciza = solid wood door

Because maciza agrees with madera, and madera is a feminine noun.

In Spanish, adjectives usually agree in gender and number with the noun they describe:

• madera maciza = feminine singular
• muebles macizos = masculine plural
• puertas macizas = feminine plural

So maciza changes form to match madera.

Because in Spanish, adjectives usually come after the noun.

So:

• madera maciza
• coche nuevo
• casa grande

This is the normal order in Spanish. Sometimes adjectives can come before the noun, but that usually adds a special nuance or emphasis. In this case, madera maciza is the standard, natural order.

Not necessarily. It means that the piece of furniture includes solid wood, so solid wood is one of its materials or components.

If you wanted to say it is made entirely of solid wood, Spanish would more clearly use something like:

• Es de madera maciza = It is made of solid wood
• Está hecho de madera maciza = It is made of solid wood

So incluye madera maciza is a bit broader than is solid wood.

Usually it stays right after the noun it describes:

• El mueble de segunda mano incluye madera maciza.

That is the clearest and most natural position. In theory, Spanish word order can move things around more than English, but here the normal order is best because de segunda mano directly modifies mueble.

The original sentence is correct, but in product descriptions Spanish often prefers wording such as:

• El mueble de segunda mano está hecho de madera maciza.
• Este mueble de segunda mano incluye partes de madera maciza.
• Mueble de segunda mano con madera maciza.

The best option depends on the exact meaning:

• if it is fully solid wood: está hecho de madera maciza
• if only some parts are solid wood: incluye madera maciza or incluye partes de madera maciza