gongyeonjang apeseo jureul seoseo ipjanghaesseo.

공연장 means a performance venue.

• 공연 = performance, show
• 장 = place, venue

So it can refer to a concert hall, theater, live venue, or another place where performances are held. It is a fairly general word.

Because -에서 marks the place where an action happens.

In this sentence, the action of lining up happened in front of the venue, so 앞에서 is natural.

• 앞에 = in front of, at the front of
• 앞에서 = in front of, at the place where something happens

A simple way to think of it:

• 앞에 often describes location
• 앞에서 often describes where an action takes place

줄을 서다 means to stand in line, to line up, or to queue.

Literally:

• 줄 = line
• 서다 = to stand

But as a full expression, 줄을 서다 is just the normal Korean way to say line up.

Because 줄을 서다 is a fixed expression.

Even though it may look strange if you translate word-for-word, Korean commonly uses 줄을 서다 to mean to form/join a line. The 을 is part of that expression.

So learners should usually remember it as one unit:

• 줄을 서다 = to line up

It comes from the verb 서다 plus the connecting ending -어서.

• dictionary form: 서다
• stem: 서-
• connected form: 서서

So 서서 here is not random repetition. It is the normal connected form meaning something like:

• by standing in line
• after lining up
• and then lined up / entered

In this sentence, 줄을 서서 links the first action to the next one.

Here -서 connects two actions:

1. 줄을 서다 = line up
2. 입장하다 = enter

So the sentence gives the sense of:

• I lined up and entered
• I entered after standing in line

It shows that the actions are closely connected. The entering happened as the next step after lining up.

Yes, 줄을 서고 입장했어 is grammatically possible, but the nuance is a little different.

• -고 simply links actions: and
• -서 often feels more connected: after, by doing that, or as part of one flow of events

So 줄을 서서 입장했어 sounds very natural for a sequence like: line up first, then enter.

입장하다 is more formal and is often used for:

• entering a venue
• entering an event
• being admitted through an entrance

들어가다 just means to go in / enter in a general sense.

So with a place like 공연장, 입장하다 sounds very natural because it suggests official entry as an audience member.

했어 is the plain informal past form.

Since 입장하다 is a 하다 verb:

• 입장하다 = to enter
• 입장했어 = entered / did enter

This style is used with:

• friends
• people younger than you
• casual conversation
• diary-style writing

More polite versions would be:

• 입장했어요 = polite
• 입장했습니다 = formal

The subject is omitted, which is very common in Korean.

So the sentence could mean:

• I lined up and entered
• we lined up and entered
• they lined up and entered

The exact subject depends on context. In isolated example sentences, English often uses I because that is the most natural default.

Most directly, it describes the location of lining up.

So the clearest reading is:

• In front of the venue, I lined up
• then I entered

But in natural Korean, a phrase like 공연장 앞에서 can also set the scene for the whole event. So it is fine even though the actual entering happens at the entrance or inside.

For learners, 줄을 서서 is the safest form to remember.

In casual writing or speech, you may also see 줄 서서, which is very common in real life. But 줄을 서다 / 줄을 서서 clearly shows the full structure and is very useful when learning the grammar.