Tôi đã viết thiệp xong rồi, nhưng tôi chưa đặt xe để về nhà.

Đã is a time/aspect marker. It often shows that an action happened before now, so in many cases it corresponds to English past forms like did, have, or have already.

In Tôi đã viết thiệp xong rồi, đã helps show that the writing action is completed in the past relative to the current moment.

However, Vietnamese does not force tense marking the way English does. Depending on context, speakers can sometimes leave out đã if the time is already clear.

They are similar, but they do different jobs.

• xong means finished or completed
• rồi often adds the sense of already or confirms that a state/change has been reached

So:

• viết xong = finish writing
• viết xong rồi = have finished writing already

Using both makes the completion very clear and natural in speech. It sounds a bit like emphasizing that the task is truly done.

Yes. Tôi đã viết thiệp rồi is natural and means I already wrote the card or I’ve written the card already.

Adding xong emphasizes completion of the task:

• đã viết thiệp rồi = the writing happened already
• đã viết thiệp xong rồi = the card-writing is completely finished

So xong is not required, but it adds a clear finished nuance.

Thiệp usually means card, especially something like:

• a greeting card
• an invitation card
• a thank-you card
• a holiday card

So viết thiệp means write a card. In context, it usually means writing the message inside the card, not physically creating the card from scratch.

Vietnamese basic word order is usually Subject + Verb + Object, much like English.

So:

• Tôi = I
• viết = write
• thiệp = card

That gives Tôi viết thiệp = I write a card / I’m writing a card.

Putting thiệp before viết would not work for this meaning.

Chưa means not yet. It is used when something has not happened up to now, but it may still happen later.

So:

• Tôi chưa đặt xe = I haven’t booked a ride yet

By contrast:

• Tôi không đặt xe = I do not book a ride / I am not booking a ride

So chưa is the right choice because the sentence means the speaker still has not done it, not that they refuse or never do it.

Đặt means book, reserve, or arrange.
Xe literally means vehicle, but in this context đặt xe usually means:

• book a taxi
• book a car
• order a ride
• arrange transportation

In modern everyday Vietnamese, this can also refer to booking a ride through an app.

Here để means in order to or for the purpose of.

So:

• đặt xe để về nhà = book a ride to go home

It links the action and its purpose:

• đặt xe = book a ride
• để về nhà = in order to go home

This is very common in Vietnamese.

Yes, if the context already makes the destination obvious.

For example:

• Tôi chưa đặt xe. = I haven’t booked a ride yet.

But if you want to make it clear that the ride is specifically for going home, then để về nhà is helpful and natural.

Yes, về nhà usually means go home or return home.

• về = return/go back
• nhà = home/house

Together, về nhà is a very common expression for going home. In many situations, về already carries the idea of returning to one’s place.

Vietnamese often repeats the subject for clarity, especially when two clauses are joined.

So:

• Tôi đã viết thiệp xong rồi, nhưng tôi chưa đặt xe để về nhà.

This is completely natural.

You could sometimes omit the second tôi in casual speech if the subject is obvious, but repeating it is clearer and more standard.

In this sentence, yes, nhưng means but and contrasts two ideas:

• one thing is finished
• another thing has not been done yet

So the structure is:

• I’ve already finished writing the card, but I haven’t booked a ride home yet.

That is a very typical use of nhưng.

Yes, it sounds natural and conversational.

A speaker might say it exactly this way to mean:

• one task is done
• another task is still unfinished

You may also hear slightly shorter versions, such as:

• Tôi viết thiệp xong rồi, nhưng chưa đặt xe về nhà.
• Tôi đã viết thiệp rồi, nhưng chưa đặt xe về nhà.

These are also natural, depending on context and speaking style.