Feldíszítjük a szobát a girlanddal.

Fel- is a verb prefix. In this sentence, it adds the idea of decorating something up, often with a sense of completeness or making it festive.

• díszít = to decorate
• feldíszít = to decorate up, to adorn, to decorate fully

So Feldíszítjük a szobát sounds more like We decorate the room up / We’ll decorate the room nicely, not just We decorate the room in a general sense.

This kind of prefix is very common in Hungarian, and it often changes the nuance of the verb.

Because Hungarian is using the definite conjugation here.

The direct object is a szobát = the room, which is definite.
When the object is definite, Hungarian often uses a special set of verb endings.

Compare:

• díszítünk = we decorate something indefinite / in general
• díszítjük = we decorate it / the specific thing

So:

• Díszítünk egy szobát. = We decorate a room.
• Díszítjük a szobát. = We decorate the room.

That is why -jük appears here.

Because szobát is in the accusative case, which marks the direct object of the verb.

• szoba = room
• szobát = room + -t = the room as the thing being decorated

In this sentence, the room is what receives the action, so it needs the accusative ending:

• Feldíszítjük a szobát. = We decorate the room.

A very common pattern in Hungarian is:

• noun in dictionary form
• add -t when it is the direct object

This is because of the -val / -vel ending, which means with.

The basic ending is:

• -val
• -vel

But when this suffix is added, the v often assimilates to the final consonant of the noun. That means the consonant gets doubled instead.

So:

• girland + val
• becomes girlanddal

The d is doubled in spelling and pronunciation.

Other examples:

• kéz + zel → kézzel = with a hand
• ház + zal → házzal = with a house
• vonat + tal → vonattal = with a train

So a girlanddal means with the garland.

Girlanddal is in the instrumental-comitative case, formed with -val / -vel.

In this sentence, it tells you what is used to decorate the room:

• a girlanddal = with the garland

So the structure is:

• feldíszítjük = we decorate up
• a szobát = the room
• a girlanddal = with the garland

This case can mean:

• with something as a tool or means
• together with someone

Here it is the instrument/tool sense: the garland is what is used in decorating.

Because both nouns are definite singular nouns:

• a szobát = the room
• a girlanddal = with the garland

Hungarian uses a / az as the definite article, like English the.

Which one appears depends on the next sound:

• a before a consonant
• az before a vowel

Since szoba and girland both begin with consonants, Hungarian uses a in both places.

Formally, the verb is in the present tense:

• feldíszítjük = we decorate / we are decorating

But Hungarian very often uses the present tense to talk about the future, especially when the context already makes the future meaning clear.

So depending on context, this could mean:

• We are decorating the room with the garland.
• We will decorate the room with the garland.

Since you said the meaning is already shown to the learner, the important grammar point is that Hungarian does not always need a separate future form where English would use will.

Yes, Hungarian verb prefixes can be attached or separated, depending on sentence structure.

In a neutral affirmative statement, the prefix is usually attached:

• Feldíszítjük a szobát.

But it can be separated in some situations, for example:

1. Negation

   • Nem díszítjük fel a szobát. = We are not decorating the room.

2. Focus

   • A szobát díszítjük fel. = It is the room that we are decorating.
   • A girlanddal díszítjük fel a szobát. = It is with the garland that we decorate the room.

So in your sentence, the attached form is the normal neutral one.

Yes. Hungarian word order is more flexible than English word order, but changing it often changes the focus or emphasis.

Your sentence:

• Feldíszítjük a szobát a girlanddal.

This is a fairly neutral way to say it.

Other possible orders include:

• A szobát feldíszítjük a girlanddal.
  This gives more attention to the room.

• A girlanddal feldíszítjük a szobát.
  This gives more attention to the garland.

• A girlanddal díszítjük fel a szobát.
  Stronger focus on with the garland.

So the sentence can change word order, but not randomly: each version can shift what sounds most important.

It is first person plural:

• we decorate
• specifically, we decorate it / the definite object

The ending -juk / -jük here tells you:

• first person plural = we
• definite conjugation

So feldíszítjük means roughly we decorate it / we decorate the specific thing.

No, girland is a loanword. It means garland or festive decorative strand.

Hungarian uses many loanwords, especially for objects, fashion, decoration, technology, and culture. Even though the word is borrowed, it still behaves like a normal Hungarian noun and takes Hungarian endings:

• girland
• girlandot = garland as a direct object
• girlanddal = with the garland

So once a borrowed noun enters Hungarian, it usually follows regular Hungarian grammar.