Πριν έρθουν οι καλεσμένοι, στολίζω το σαλόνι με λουλούδια.

Greek often drops subject pronouns because the verb ending already shows who is doing the action.
Here, στολίζω ends in -ω, which tells you the subject is I.

So:

• στολίζω = I decorate / I am decorating

You could add εγώ for emphasis, but it is not necessary:

• Εγώ στολίζω το σαλόνι... = I decorate the living room...

Here πριν means before and introduces a time clause:

• Πριν έρθουν οι καλεσμένοι = Before the guests come / arrive

In this kind of structure, Greek normally uses πριν with the subjunctive to refer to an action that is expected or not yet completed from the speaker’s point of view.

Yes — πριν να έρθουν is also possible.

In Modern Greek, after πριν, να is often omitted, especially in everyday language. So both of these can be natural:

• πριν έρθουν οι καλεσμένοι
• πριν να έρθουν οι καλεσμένοι

The version without να is very common and sounds perfectly normal.

Έρθουν is the 3rd person plural aorist subjunctive of έρχομαι.

So it means:

• they come
• they arrive

in a subjunctive environment such as after πριν.

Even though it is built from the aorist stem, it is not automatically past tense here. In Greek, the aorist vs. present contrast in the subjunctive is mainly about aspect.

Because Greek is viewing the guests’ arrival as one whole event.

• έρθουν = a single completed arrival, seen as a whole
• a present-subjunctive idea would suggest something more ongoing, repeated, or in progress

So πριν έρθουν οι καλεσμένοι means before the guests arrive, with the arrival treated as one event. That is the natural choice here.

It can mean either, depending on context.

Greek present tense is broader than English and can describe:

• a habit or routine: I decorate the living room before the guests come
• something happening now: I am decorating the living room
• sometimes a vivid, narrative present

In this sentence, without more context, it most naturally sounds like a habitual or general statement. If you wanted a clear one-time future meaning, Greek would often use:

• Θα στολίσω το σαλόνι με λουλούδια πριν έρθουν οι καλεσμένοι.

Literally, καλεσμένος means invited or an invited person.

So:

• ο καλεσμένος = the invited man / the guest
• οι καλεσμένοι = the invited people / the guests

This is very common in Greek: an adjective or participle can be used like a noun when the article is present.
So οι καλεσμένοι is a normal way to say the guests.

Because Greek word order is more flexible than English word order.

Both of these are possible:

• πριν έρθουν οι καλεσμένοι
• πριν οι καλεσμένοι έρθουν (much less natural here)

Greek very often puts the subject after the verb, especially in subordinate clauses or when the subject is already understood from context. So έρθουν οι καλεσμένοι sounds natural.

Το σαλόνι is the direct object of στολίζω, so it is in the accusative.

You are decorating what?

• το σαλόνι = the living room

Because σαλόνι is a neuter noun, its nominative and accusative forms are the same, so you do not see a visible change here. The article το is also the same in nominative and accusative singular neuter.

Because Greek uses the pattern:

• στολίζω κάτι με κάτι = I decorate something with something

So:

• στολίζω το σαλόνι με λουλούδια = I decorate the living room with flowers

The preposition με means with and takes the accusative in Modern Greek.

Because λουλούδια here means flowers in a general, non-specific sense.

• με λουλούδια = with flowers / with some flowers
• με τα λουλούδια = with the flowers, meaning specific flowers already known in the conversation

Greek often leaves out the article with plural nouns when speaking generally or nonspecifically, especially after prepositions like με.

Yes. Greek word order is fairly flexible.

For example, you could also say:

• Στολίζω το σαλόνι με λουλούδια πριν έρθουν οι καλεσμένοι.

That means the same thing. The version with Πριν έρθουν οι καλεσμένοι first puts more focus on the timing: it sets the scene first, then tells you the main action.

Because the sentence begins with a subordinate time clause:

• Πριν έρθουν οι καλεσμένοι, ...

In Greek, when this kind of clause comes first, it is normally separated from the main clause by a comma.

If the main clause comes first, the comma is often not needed:

• Στολίζω το σαλόνι με λουλούδια πριν έρθουν οι καλεσμένοι.

Yes, στολίζω is a very common everyday verb for decorate, especially when you make something look nice or festive.

It often suggests decoration for an occasion, celebration, or pleasant appearance. Another word is διακοσμώ, but that often sounds more formal or more like decorate/design in a general sense.

So in this sentence, στολίζω is a very natural choice.