jumareneun baekhwajeomi neomu bokjaphaeseo onraineuro jumunhaeyo.

-에 marks the time when something happens, so 주말에 means on the weekend / on weekends.

Adding -는 makes it a topic or contrast marker:

• 주말에 = on weekends
• 주말에는 = as for weekends / on weekends (in particular)

So 주말에는 often implies a contrast such as:

• on weekends, it’s crowded, so I order online
• maybe on weekdays, I do something different

In natural Korean, 주말에는 sounds very common when setting the scene or contrasting one situation with another.

Here, 백화점이 is the subject of 복잡하다 (to be crowded/complicated).

The sentence structure is basically:

• 주말에는 = on weekends
• 백화점이 너무 복잡해서 = department stores are too crowded, so...
• 온라인으로 주문해요 = I order online

So 이/가 marks what is crowded: the department store.

A native English speaker may expect something like I find the department store crowded, but Korean often states the condition directly:

• 백화점이 복잡하다 = the department store is crowded

Usually not here. Although 복잡하다 can mean complicated in some contexts, with places it usually means:

• crowded
• busy
• packed
• congested

So in this sentence, 백화점이 너무 복잡해서 means the department store is too crowded or so crowded.

Context decides the meaning:

• 문제가 너무 복잡해요 = the problem is too complicated
• 길이 너무 복잡해요 = the roads are very congested / confusing
• 백화점이 너무 복잡해요 = the department store is very crowded

It can feel like either too or very, depending on context.

In this sentence, because it is followed by -아서/해서 expressing a reason, 너무 strongly suggests:

• too
• so
• very

So the whole phrase means something like:

• because the department store is too crowded
• because it’s so crowded at department stores

In everyday Korean, 너무 is also often used casually just to mean very, even when there is no negative idea.

-아서/어서/해서 connects two clauses and usually means:

• because
• so
• and so

Here:

• 복잡하다 → 복잡해서
• too crowded, so / because it’s crowded

So the sentence means:

• Because department stores are too crowded on weekends, I order online.

A useful point:

• 해서 is the form used with 하다 verbs/adjectives
• 복잡하다 ends in 하다, so 복잡해서 is the natural result

-으로 often shows the means, method, or direction:

• by
• through
• via

So 온라인으로 주문해요 means:

• I order online
• I order through an online method/channel

This is very natural Korean.

Compare:

• 온라인으로 주문해요 = I order online / via the internet
• 인터넷으로 주문해요 = I order through the internet
• 앱으로 주문해요 = I order using an app

You may also hear 온라인에서 주문해요, which focuses more on the place/platform where the action happens: on an online site/platform. But 온라인으로 주문해요 is very common when emphasizing the method.

Because 주문하다 means to order, and ordering online is often expressed as placing an order rather than simply buying.

So:

• 사다 = to buy
• 주문하다 = to order

Examples:

• 가게에서 옷을 사요 = I buy clothes at a store
• 온라인으로 옷을 주문해요 = I order clothes online

In English, buy online and order online can both work, but Korean often prefers 주문하다 when talking about making an online purchase.

Korean often drops information that is obvious from context.

So even though the sentence does not say what is being ordered, that is perfectly natural. The meaning is still complete:

• 온라인으로 주문해요 = I order online

In real conversation, speakers often omit:

• the object
• the subject
• sometimes other predictable information

If you wanted to include the object, you could say:

• 주말에는 백화점이 너무 복잡해서 옷을 온라인으로 주문해요. = On weekends, department stores are too crowded, so I order clothes online.

Usually it sounds like a general habit.

Because:

• 주말에는 often means on weekends
• 주문해요 is present polite style, which can describe habitual action

So the natural interpretation is:

• On weekends, department stores are too crowded, so I order online.

If the speaker meant one specific weekend, context would normally make that clear.

Korean is basically an SOV language:

• Subject – Object – Verb

More importantly, the main verb usually comes at the end of the clause or sentence.

So in:

• 주말에는 백화점이 너무 복잡해서 온라인으로 주문해요

the final verb 주문해요 tells you the main action:

• I order

Everything before it sets up the time, reason, and method:

• 주말에는 = on weekends
• 백화점이 너무 복잡해서 = because department stores are too crowded
• 온라인으로 = online / via online

This sentence order can feel backward to English speakers at first, but it is completely normal in Korean.

Yes. Korean often uses a singular-looking noun to talk about something in a general sense.

So 백화점이 너무 복잡해서 can naturally mean:

• department stores are too crowded not necessarily just one specific department store.

This is very common in Korean. Number is often left unstated unless it matters.

주문해요 is in the 해요-style, which is:

• polite
• common in everyday conversation
• less formal than 합니다 style

So it is appropriate for:

• normal conversation
• speaking politely to someone you do not know very well
• many casual written situations

Compare:

• 주문해요 = polite everyday style
• 주문합니다 = more formal
• 주문해 = casual/informal

Yes, but the feel changes slightly.

Original:

• 주말에는 백화점이 너무 복잡해서 온라인으로 주문해요.
• This is one smooth sentence: Because it’s crowded, I order online.

With 그래서:

• 주말에는 백화점이 너무 복잡해요. 그래서 온라인으로 주문해요.
• This becomes two sentences: Department stores are very crowded on weekends. So I order online.

Both are natural. The -해서 version sounds more connected and compact.