La flor roja forma parte de la decoración de la sala.

Because flor is a feminine noun in Spanish, so it takes the feminine article la and the feminine form of the adjective, roja.

A key point for English speakers: noun gender in Spanish is not always predictable from the ending. Even though many feminine nouns end in -a, some feminine nouns do not, and flor is one of them.

So:

• la flor = the flower
• roja = red, in feminine singular form

They have to match:

• la flor roja
• not el flor rojo

In Spanish, descriptive adjectives often come after the noun, unlike in English.

So:

• English: the red flower
• Spanish: la flor roja

This is the most normal word order here. Spanish can sometimes place adjectives before the noun, but that usually changes the tone, emphasis, or style. For a basic descriptive sentence, noun + adjective is the standard pattern.

Because adjectives in Spanish usually agree with the noun in gender and number.

Here:

• flor is feminine singular
• so the adjective must also be feminine singular
• rojo becomes roja

Compare:

• el libro rojo = the red book
• la flor roja = the red flower
• las flores rojas = the red flowers

Yes. Formar parte de is a very common expression meaning to be part of or to make up part of.

In this sentence:

• La flor roja forma parte de la decoración de la sala.
• literally: The red flower forms part of the decoration of the room
• natural English: The red flower is part of the room’s decoration / The red flower is part of the decor in the room

So you should learn formar parte de as a chunk:

• formo parte de = I am part of
• formas parte de = you are part of
• forma parte de = he/she/it is part of

Because the subject is La flor roja, which is singular.

The verb has to agree with the subject:

• La flor roja forma... = The red flower is part of...
• Las flores rojas forman... = The red flowers are part of...

Even though there are several nouns later in the sentence, the main subject is only la flor roja.

Because each de connects a different idea.

1. parte de la decoración

   • parte de = part of
   • So the flower is part of the decoration

2. la decoración de la sala

   • this means the decoration of the room or the room’s decoration
   • Here, de shows what the decoration belongs to or is associated with

So the structure is:

• [La flor roja]
  subject

• [forma parte de]
  verb expression = is part of

• [la decoración de la sala]
  what it is part of

Spanish often uses definite articles (el, la, los, las) more often than English does.

Here:

• la decoración = the decoration / the decor
• la sala = the room / the living room

Even if English might sometimes say part of room decor, Spanish normally prefers the article:

• parte de la decoración de la sala

Also, both decoración and sala are feminine nouns, so they take la.

In Latin American Spanish, sala often refers to the living room or sitting room. In some contexts, it can also mean a more general room or hall.

So la decoración de la sala will often be understood as:

• the living room decor
• the decoration of the living room

The exact translation depends on context, but living room is a very common interpretation in Latin America.

The accent mark shows which syllable is stressed: de-co-ra-CIÓN.

This is important because Spanish stress follows rules, and the accent mark tells you that the stress falls on the last syllable.

Also, many nouns ending in -ción have this pattern:

• decoración
• nación
• información
• situación

A useful pattern:

• English words ending in -tion often correspond to Spanish words ending in -ción

You can, but it is not the most neutral or everyday wording.

• la flor roja = normal, standard description
• la roja flor = more literary, poetic, or emphatic

For most learners, la flor roja is the form you should use in ordinary speech and writing.

You actually can say es parte de, and it means almost the same thing.

Compare:

• La flor roja es parte de la decoración de la sala.
• La flor roja forma parte de la decoración de la sala.

Both are correct.

However, formar parte de is a very common set phrase and often sounds a bit more natural or formal in this kind of sentence.
So forma parte de is a great expression to learn and reuse.

It would become:

Las flores rojas forman parte de la decoración de la sala.

Here is what changes:

• la → las
• flor → flores
• roja → rojas
• forma → forman

This shows agreement across the sentence:

• noun changes to plural
• adjective changes to plural
• verb changes to plural

That agreement is one of the most important grammar patterns in Spanish.