Când am ajuns acolo, eu alesesem deja muzica, iar Andrei pregătise cafeaua.

Because the sentence describes two layers of past time:

• Când am ajuns acolo = the moment of arrival
• eu alesesem deja muzica and Andrei pregătise cafeaua = actions completed before that arrival

So Romanian uses:

• perfectul compus: am ajuns = I arrived / I got there
• mai mult ca perfectul: alesesem, pregătise = had chosen, had prepared

This is very similar to English using arrived vs. had chosen / had prepared.

Am ajuns is perfectul compus.

It is formed with:

• the auxiliary am from a avea
• the past participle ajuns

So:

• a ajunge = to arrive / to reach
• am ajuns = I arrived / I have arrived

In this sentence, it sets the reference point in the past: the speaker arrived, and by that time the other actions were already finished.

They are both mai mult ca perfectul, the Romanian pluperfect.

They mean:

• alesesem = I had chosen
• pregătise = he had prepared

This tense shows an action that happened before another past action.

So:

• am ajuns = later past action
• alesesem / pregătise = earlier past actions

Romanian mai mult ca perfectul is usually a single-word tense, unlike English had + participle.

Examples from the sentence:

• alesesem = I had chosen
• pregătise = he had prepared

Very roughly, it is built from the verb stem used in older past forms plus special endings such as:

• -sem
• -seși
• -se
• -serăm
• -serăți
• -seră

So:

• eu alesesem = I had chosen
• el/ea pregătise = he/she had prepared

For learners, the most important thing is usually to recognize this tense as had done.

Yes, it could be left out.

Romanian often omits subject pronouns because the verb form already shows the person:

• alesesem already means I had chosen

So the sentence could also be:

• Când am ajuns acolo, alesesem deja muzica, iar Andrei pregătise cafeaua.

Including eu adds emphasis or contrast. It can suggest something like:

• I had already chosen the music, and Andrei had prepared the coffee.

So eu is not required for grammar, but it can be useful for focus.

Iar is a coordinating conjunction. In this sentence it means something like:

• and
• while
• whereas

Here it connects two parallel past actions:

• eu alesesem deja muzica
• Andrei pregătise cafeaua

So iar gives a slight sense of contrast or parallel distribution:

• I had chosen the music, while/and Andrei had prepared the coffee.

It is not exactly the same as și every time.

• și = simple and
• iar = and/while, often with a slight contrast or balancing effect

Because Romanian usually attaches the definite article to the end of the noun.

So:

• muzică = music
• muzica = the music

and

• cafea = coffee
• cafeaua = the coffee

This is one of the big differences from English. Instead of a separate word like the, Romanian often uses an ending attached to the noun.

In this sentence, both nouns are understood as specific:

• muzica = the music that was to be played / the playlist / the music selection
• cafeaua = the coffee that Andrei had prepared

Deja means already.

In the sentence:

• eu alesesem deja muzica

it comes after the verb and before the noun phrase, which is very natural.

Romanian word order is fairly flexible, so you may also hear:

• eu deja alesesem muzica

Both are possible, but:

• alesesem deja muzica often sounds very natural in neutral narration
• deja alesesem muzica can put slightly more focus on already

So the placement affects emphasis more than basic meaning.

Yes. Romanian word order is more flexible than English word order.

The original sentence is neutral and natural:

• Când am ajuns acolo, eu alesesem deja muzica, iar Andrei pregătise cafeaua.

But other versions are possible, for example:

• Când am ajuns acolo, deja alesesem muzica, iar Andrei pregătise cafeaua.
• Eu alesesem deja muzica când am ajuns acolo, iar Andrei pregătise cafeaua.

The meaning stays mostly the same, but the focus changes slightly.

Romanian often moves elements around for emphasis, rhythm, or style.

Because Când am ajuns acolo is an introductory subordinate clause.

It functions like:

• When I got there, ...

Romanian normally separates this kind of introductory time clause with a comma:

• Când am ajuns acolo, ...

This is very similar to English punctuation when the when-clause comes first.

It is natural and correct Romanian.

The pluperfect (mai mult ca perfectul) is absolutely appropriate when you want to show that one past action happened before another past action.

That said, in very casual speech, some speakers may prefer simpler past forms and let context show the sequence. But the version in your sentence is:

• clear
• precise
• grammatically strong
• very normal in narration or careful speech

So a learner should recognize it as good, standard Romanian.

Because the sentence refers to a specific, identifiable thing, not just any music.

• o muzică would usually mean a piece of music / some music in a less specific sense
• muzica means the music, the one relevant in the situation

Here the speaker is talking about the music chosen for that moment or event, so the definite form fits naturally.

The same logic applies to cafeaua:

• not just some coffee
• but the coffee that had been prepared

Yes. Romanian verb endings often make the subject clear on their own.

For example:

• alesesem = I had chosen
• pregătise = he/she had prepared
• am ajuns = I arrived / I got there

That is why Romanian can often omit pronouns like eu, tu, el, noi, etc.

In this sentence:

• eu is optional because alesesem already marks first person singular
• Andrei is included because it identifies the person clearly and naturally

This is one reason Romanian sentences can sometimes look shorter or differently structured than English ones.