Wǒ zuótiān zài wǎngzhàn shàng xiàdān mǎi le yíjiàn yīfu, jīntiān jiù shōudào le.

Mandarin usually puts information in this order:

Subject + Time + Place + Verb phrase + Object

So here:

• 我 = subject
• 昨天 = time
• 在网站上 = place/location of the action
• 下单买了 = verb phrase
• 一件衣服 = object

That is why 我昨天在网站上... sounds natural.

A very common pattern is:

我 + 时间 + 在/从/到 + 地点 + 动作

So this sentence follows a very standard Mandarin word order.

在网站上 means on the website.

Breakdown:

• 在 = at / in / on
• 网站 = website
• 上 = on / above / attached to the surface or platform

In Mandarin, many nouns that act like locations often take a localizer such as:

• 上 = on
• 里 = in / inside
• 下 = under

So:

• 在桌子上 = on the table
• 在车里 = in the car
• 在网站上 = on the website

Even though a website is not a physical surface, Mandarin still uses 上 in this kind of expression.

They are related, but not exactly the same.

• 买 = to buy
• 下单 = to place an order

So 下单买了一件衣服 literally suggests something like:

placed an order to buy a piece of clothing

Using both can make the action feel more specific, especially in online shopping:

1. you place the order
2. you buy the item through that order

In everyday speech, this is natural. But depending on context, people might also say:

• 我昨天在网站上买了一件衣服。
• 我昨天在网站上下单了一件衣服。

Those are also fine.

The 了 after 买 marks the action as completed.

So:

• 买 = buy
• 买了 = bought

Here it tells you that the buying/ordering happened and was completed in the past.

Important point: 了 does not simply mean past tense the way English does. It usually marks completion or a change of situation.

So 买了 focuses on the fact that the action of buying was completed.

Because there are two completed events:

1. 买了 = bought / placed the order
2. 收到了 = received it

Each 了 belongs to its own verb phrase.

So the sentence is basically:

• Yesterday I ordered and bought a piece of clothing on a website
• and today I already received it

It is completely normal in Mandarin to have more than one 了 in a sentence if more than one action is being presented as completed.

Yes.

• 收 = to receive / accept / collect
• 收到 = to receive successfully

The 到 here is a result complement. It shows that the action reached its result.

So:

• 我收了一个包裹 can mean I accepted/took in a package
• 我收到了一个包裹 clearly means I received a package

In this sentence, 收到了 emphasizes that the clothing actually arrived.

In Mandarin, the object can be omitted if it is obvious from context.

Earlier in the sentence, we already learned that the speaker bought 一件衣服. So in 今天就收到了, the listener naturally understands:

today I already received it

The omitted object is basically 那件衣服 or 它.

This kind of omission is very common in Chinese when the meaning is clear.

Here 就 means something like:

• as early as
• already
• so soon
• then

It often shows that something happened earlier than expected or more quickly than expected.

So:

• 今天收到了 = I received it today.
• 今天就收到了 = I received it today already / as early as today / surprisingly quickly.

In this sentence, 就 adds the feeling that the delivery was fast.

件 is a measure word for certain items, especially:

• clothing
• matters/cases
• some abstract things

In Mandarin, numbers usually need a measure word before a noun.

So:

• 一件衣服 = one piece/item of clothing
• 两件衣服 = two pieces of clothing

You cannot normally say just 一衣服. You need the measure word:

一 + 件 + 衣服

This is because of a tone change rule for 一.

Normally:

• 一 is pronounced yī

But when it comes before a 4th-tone syllable, it changes to 2nd tone:

• 一件 → yí jiàn because 件 is 4th tone

Very common examples:

• 一天 = yì tiān because 天 is 1st tone
• 一年 = yì nián because 年 is 2nd tone
• 一件 = yí jiàn because 件 is 4th tone

So the written character stays 一, but the pronunciation changes.

The second syllable of 衣服 is usually in the neutral tone in everyday Mandarin.

So it is commonly pronounced:

• yīfu

not strongly as:

• yīfú

This is very common in everyday vocabulary. Many two-syllable words have a neutral second syllable in normal speech.

So if you hear yīfu, that is the standard natural pronunciation.

A natural way to understand it is:

• I got it today already
• It arrived as early as today
• I received it today, so quickly

Word by word:

• 今天 = today
• 就 = already / as early as / unexpectedly soon
• 收到 = receive
• 了 = completed action

So the whole clause is not just about time; it also carries a feeling of surprise at the speed.

Yes, it strongly suggests online shopping.

Clues:

• 在网站上 = on a website
• 下单 = place an order

Those words are very commonly used for shopping online.

So this sentence does not just mean I bought clothes in a general sense. It specifically suggests:

I ordered a piece of clothing on a website yesterday, and it already arrived today.

Yes, absolutely.

That version is very natural too.

Difference:

• 在网站上 = on a website
• 在网上 = online / on the internet

So:

• 在网站上 is a bit more specific
• 在网上 is broader and more general

Both work well in this context.

The comma separates two related clauses:

1. 我昨天在网站上下单买了一件衣服
2. 今天就收到了

This helps show the sequence clearly:

• first, the order was placed yesterday
• then, the item was received today

Mandarin often uses commas to connect closely related actions or events, especially when the subject stays the same and the meaning flows naturally from one clause to the next.