Tôi sẽ đến bữa tiệc sinh nhật của Lan sau khi làm xong việc ở văn phòng.

Sẽ is a future marker, similar to will in English.

• Tôi sẽ đến... = I will come / I will go...
• It tells you the action has not happened yet.

Vietnamese often leaves out sẽ if the time is already clear from context, but including it makes the future meaning more explicit.

Đến means to arrive at / to come to / to go to a destination. In this sentence, it focuses on reaching the party.

• đến bữa tiệc = come to / go to the party

Đi is a more general word for go.
So:

• Tôi sẽ đi đến bữa tiệc... is possible, but less natural here
• Tôi sẽ đến bữa tiệc... sounds smoother and more common

In many cases, Vietnamese uses đến where English would simply say go to.

This is a noun phrase built in a very common Vietnamese way.

• bữa tiệc = party, meal gathering, banquet
• sinh nhật = birthday

Put together:

• bữa tiệc sinh nhật = birthday party

Vietnamese often places the main noun first and then adds words that describe it.

So the structure is roughly:

• bữa tiệc = the party
• sinh nhật = specifically, a birthday party

Vietnamese usually shows possession with của, and the possessor comes after the noun.

• bữa tiệc sinh nhật của Lan = Lan’s birthday party
• literally: birthday party of Lan

This is different from English, where possession often comes first:

• English: Lan’s birthday party
• Vietnamese: birthday party of Lan

Sau khi means after.

It introduces an action that happens earlier than the main action.

In this sentence:

• Tôi sẽ đến bữa tiệc... sau khi làm xong việc ở văn phòng
• I will go to Lan’s birthday party after finishing work at the office

So the order of events is:

1. finish work
2. go to the party

Làm xong means finish doing or do something completely.

• làm = do
• xong = finished, completed

Together they form a very common pattern:

• verb + xong = finish doing that verb

Examples:

• ăn xong = finish eating
• viết xong = finish writing
• làm xong = finish doing / finish working on

So làm xong việc means finish the work.

Both can relate to work, but they are used a little differently.

• việc often means work, task, or things to do
• công việc often means job, work, or occupation, though it can also mean a task

In this sentence, làm xong việc is a very natural expression meaning:

• finish the work
• finish what I need to do

You could also hear làm xong công việc, which is also correct, but làm xong việc sounds very common and natural in everyday speech.

Ở văn phòng means at the office, and it most naturally describes where the work is being done.

So this part means:

• làm xong việc ở văn phòng = finish work at the office

It does not mean the birthday party is at the office.
It modifies việc / làm xong việc, not bữa tiệc sinh nhật.

Vietnamese often omits the subject when it is already clear from context.

In this sentence, the subject of both actions is Tôi:

• Tôi sẽ đến...
• (Tôi) làm xong việc ở văn phòng

Because it is obvious that the same person is finishing work and then going to the party, Vietnamese leaves out the second Tôi.

A fuller version would be:

• Tôi sẽ đến bữa tiệc sinh nhật của Lan sau khi tôi làm xong việc ở văn phòng.

This is grammatical, but the shorter version sounds more natural.

The sentence follows a very common Vietnamese structure:

• Tôi = I
• sẽ = will
• đến = come to / go to
• bữa tiệc sinh nhật của Lan = Lan’s birthday party
• sau khi làm xong việc ở văn phòng = after finishing work at the office

So the pattern is:

• Subject + future marker + verb + object/place + time clause

A very literal breakdown is:

• I will come to Lan’s birthday party after finishing work at the office.

Yes. Vietnamese đến does not always match English come and go in exactly the same way.

Depending on context, English might say:

• I will come to Lan’s birthday party...
• I will go to Lan’s birthday party...

Both can work, but go is often the more natural default in English unless the speaker is thinking from the destination’s point of view.

So even though đến often literally means come to / arrive at, the best English translation may use go.

Yes, it can.

You can say:

• Sau khi làm xong việc ở văn phòng, tôi sẽ đến bữa tiệc sinh nhật của Lan.

This means the same thing:

• After finishing work at the office, I will go to Lan’s birthday party.

Putting the time clause first can make the sequence of events clearer or slightly more natural, depending on context.

Yes, it is natural and correct.

It sounds like normal spoken or written Vietnamese. A few small variations are also possible, such as:

• Tôi sẽ đến dự tiệc sinh nhật của Lan sau khi làm xong việc ở văn phòng.
• Tôi sẽ đi dự tiệc sinh nhật của Lan sau khi tan làm ở văn phòng.

But the original sentence is already perfectly good Vietnamese.