baendeuga deudieo mudaee nawasseo.

가 marks 밴드 as the subject: 밴드가 = the band / the band is the one that...

In this sentence, 가 sounds natural because it presents the band as the subject of the event: the band finally came out onto the stage.

If you used 밴드는, it would sound more like you are setting up the band as the topic, often with some contrast or background feeling:

• 밴드가 드디어 무대에 나왔어.
  = The band finally came on stage.
• 밴드는 드디어 무대에 나왔어.
  = As for the band, it finally came on stage. / possibly contrasting with something else

So 가 is the more neutral choice here.

드디어 means finally, at last, or in the end after waiting.

It adds a feeling that people were expecting or waiting for this moment.

In Korean, adverbs like 드디어 are fairly flexible in position, though some placements sound more natural than others:

• 밴드가 드디어 무대에 나왔어.
• 드디어 밴드가 무대에 나왔어.
• 밴드가 무대에 드디어 나왔어.

All are possible, but the original sentence is very natural.

무대 means stage, and 에 is a location/direction particle.

Here, 무대에 means onto the stage or to the stage.

With verbs like 나오다, 에 often marks the place someone appears in or comes out to:

• 밖에 나왔어 = came outside
• 텔레비전에 나왔어 = appeared on TV
• 무대에 나왔어 = came out onto the stage / appeared on stage

So 에 is not just static location here; with movement/appearance verbs, it can mark the destination or place of appearance.

나왔어 comes from 나오다, which literally means to come out, to appear, or to emerge.

That makes it a very natural verb for performers coming onto a stage.

Compare:

• 왔어 from 오다 = came
• 나왔어 from 나오다 = came out, appeared

For a band entering the stage in front of an audience, 나오다 sounds more natural because it gives the sense of coming out from backstage or appearing before the audience.

The dictionary form is 나오다.

It changes like this:

• 나오다
• stem: 나오-
• past tense: 나왔어

This happens because 오다 verbs often contract in the past tense:

• 오다 → 왔어
• 나오다 → 나왔어

So 나왔어 is the casual past form meaning came out or appeared.

나왔어 is the informal, casual style, often used with:

• friends
• younger people
• family
• people you are close to

More polite versions would be:

• 밴드가 드디어 무대에 나왔어요.
  polite everyday style
• 밴드가 드디어 무대에 나왔습니다.
  formal style

So the original sentence sounds like something you would say casually, like to a friend at a concert.

In this sentence, yes, 밴드 clearly means a musical band.

Korean 밴드 is a loanword from English band, but in other contexts it can sometimes mean other kinds of bands, such as a rubber band or a medical band, depending on context. Still, when paired with 무대 and 나왔어, the meaning music group is obvious.

Yes. Both are good depending on the tone you want.

• came on stage sounds direct and natural
• appeared on stage sounds a little more descriptive
• came out on stage captures the nuance of 나오다 especially well

Because 나오다 has the idea of coming out or appearing, all of these can work.

Yes. With performers, 나오다 often means to come out before the audience, to take the stage, or to appear.

So this sentence does not just mean physical movement. It can also carry the event-like feeling of the band finally made their entrance.

That is why it sounds very natural in a concert or show context.

Yes. Korean word order is flexible, especially with adverbs and prepositional phrases, as long as the particles stay correct.

For example:

• 밴드가 드디어 무대에 나왔어.
• 드디어 밴드가 무대에 나왔어.
• 무대에 밴드가 드디어 나왔어.

These all mean roughly the same thing, but the emphasis changes a little.

• Starting with 드디어 emphasizes finally
• Starting with 무대에 emphasizes the stage/location
• The original sounds balanced and very natural

Usually 무대에 나왔어 is the better choice here.

Why?

• 에 marks the destination or place of appearance: onto/on the stage
• 에서 often marks the place where an action happens

So:

• 무대에 나왔어 = came out onto the stage / appeared on stage
• 무대에서 would sound less natural with 나오다 in this exact meaning

You would use 무대에서 with other verbs such as:

• 무대에서 노래했어 = sang on stage
• 무대에서 춤췄어 = danced on stage

So with 나오다, 에 is the normal choice.