Lǎoshī bǎ jīntiān de wénjiàn shàngchuán dào wǎngzhàn le, wǒ huíjiā yǐhòu zài xiàzǎi.

把 marks the object as something being handled or disposed of by the action.

Pattern: Subject + 把 + object + verb + result/location

Here: 老师 把 今天的文件 上传到网站了 = the teacher took today’s file(s) and caused them to end up on the website.

This pattern is very common when:

• the object is specific
• the action clearly affects it
• there is a result or destination, such as 上传到网站

So 把 helps highlight what happened to the files.

Because here 今天 is modifying 文件, not 上传.

• 今天的文件 = today’s file(s) / the file(s) for today
• If you said 老师今天上传文件, then 今天 would mean today modifies the action uploaded

So the sentence is not mainly saying the teacher uploaded the files today. It is saying the teacher uploaded today’s files.

的 links a modifier to a noun.

So:

• 今天 = today
• 文件 = file/document
• 今天的文件 = today’s file(s)

This is similar to English ’s or of, depending on context.

Other examples:

• 老师的文件 = the teacher’s file(s)
• 明天的课 = tomorrow’s class

Chinese nouns usually do not show singular vs. plural by themselves.

So 文件 can mean:

• a file / document
• files / documents

You know the number from context, not from the noun form itself.

That means 今天的文件 could be:

• today’s file
• today’s files

Both are possible unless the broader context makes it clear.

到 shows the destination or endpoint of the action.

• 上传 = upload
• 上传到网站 = upload to the website

So 到 tells you where the files end up.

This is very common in Chinese:

• 放到桌子上 = put onto the table
• 发到群里 = send into the group chat
• 传到电脑里 = transfer onto the computer

In this sentence, 上传到网站 emphasizes the result: the files are now on the website.

Yes, 网站上 is possible.

• 上传到网站 = upload to the website
• 上传到网站上 = upload onto the website

Both are natural. The version without 上 is a little more concise. The version with 上 can sound slightly more explicit about the location.

So both work, but 上传到网站 is perfectly normal.

No. 了 is not simply a past-tense marker like English -ed.

Here, 了 shows that the uploading has been completed and that there is now a new situation:

• the teacher has uploaded the file(s)
• now they are available on the website

So 了 often signals:

• completion
• change of state
• a newly relevant situation

That is why it fits well here: the upload is done, and that matters for what comes next.

Use 再 for something that will happen later or after another event.

Here: 我回家以后再下载 = I’ll download it after I get home

So 再 means something like:

• then
• again later
• after that

By contrast, 又 is usually used for something that has already happened again or for repeated events viewed as actual facts.

Compare:

• 我回家以后再下载。 = I’ll download it later, after I get home.
• 我又下载了一次。 = I downloaded it again.

So 再 is the correct choice here because the downloading has not happened yet.

以后 means after and attaches to the phrase before it.

So:

• 回家 = go home
• 回家以后 = after going home / after I get home

This is a very common structure:

• 吃饭以后 = after eating
• 下课以后 = after class ends
• 到北京以后 = after arriving in Beijing

So 我回家以后再下载 literally follows the Chinese order: I go home after, then download

Natural English: I’ll download it after I get home.

Because 回家以后 here is not describing a completed past event. It is setting up a future sequence:

1. I go home
2. then I download

In this kind of time clause, Chinese often does not need 了.

So:

• 我回家以后再下载 = after I get home, I’ll download it

If you added 了, it could sometimes emphasize completion, but it is not necessary here and may sound heavier than needed.

Because the object is already clear from context.

The first clause mentions: 今天的文件

So in the second clause, Chinese can simply say: 再下载 and the listener understands that it means download the file(s).

This kind of omission is very common in Chinese when the object has already been established.

Full version: 我回家以后再下载今天的文件。

Natural shorter version: 我回家以后再下载。

You usually would not just remove 把 and keep everything else the same.

That is because 上传到网站 strongly suggests a result/destination, and 把 fits that pattern very naturally.

A plain non-把 version with the same wording may sound less natural. Native speakers often prefer 把 when:

• the object is specific
• the action changes its state or location
• the result is important

So in this sentence, 把 is one of the most natural choices.

Chinese often leaves definiteness to context.

So 老师 can mean:

• the teacher
• a teacher
• sometimes even my teacher / our teacher, if the context makes that obvious

In a sentence like this, English usually chooses the teacher, because the speaker probably has a specific teacher in mind. But Chinese does not need an article like the or a.