Learn Hardcore Chinese: wǒ bǎ diànnǎo fàng zài zhuōzi shàngmian le.

It pulls the object 电脑 in front of the verb and highlights the result the action has on it.
Pattern: Subject + 把 + Object + Verb + Result/Direction/Location + (了).
Here the result is the final location: 放在桌子上面. Without a clear result, a 把-sentence sounds incomplete.

Is the sentence-final 了 (le) just “past tense”?

No. Sentence-final 了 marks a new situation or a completed change that’s relevant now.
我把电脑放在桌子上面了 suggests: the action is done and the computer is now on the desk.
Chinese doesn’t have a true past tense; time is usually shown with time words (like 昨天) and aspect markers such as 了.

Where else can I put 了 in this sentence?

Two common options:
- Sentence-final: 我把电脑放在桌子上面了 (very common; new situation/completion).
- After the verb phrase: 我把电脑放在了桌子上面 (focus on the action’s completion).
Don’t use both here unless you have a specific nuance in mind. Either one is fine in everyday speech.

Can I say this without 把?

Yes, depending on what you want to emphasize:

Action without 把 (colloquial, common in speech): 我放电脑在桌子上(面)了.
Topic–comment: 电脑我放在桌子上(面)了 (topic is 电脑).
Just the resulting state (no actor): 电脑在桌子上了.
Describing a static scene with 着: 桌子上(面)放着一台电脑 (means “there’s a computer sitting on the desk,” not “I put it there”).

Why do we need 在 after 放? Could I drop it?

With placement verbs like 放, you typically use:
- 放在 + place to express the resulting location, or
- 放到 + place to emphasize movement toward the place.
我把电脑放在桌子上(面) and 我把电脑放到桌子上(面) are both fine.
Don’t drop 在/到: 我把电脑放桌子上 is nonstandard.

What’s the difference between 放在 and 放到?

放在 highlights the end state: it is placed there.
放到 highlights the motion or goal: it was moved/put to there.
In many contexts they’re interchangeable. If you care about the path/goal, 到 is slightly more dynamic; if you care about the resulting location, 在 is slightly more stative.

Do I need 上面 specifically? What about 上 or 桌上?

上, 上面, 上边 are largely interchangeable in everyday use here.
Shorter forms are very common:
- 桌子上 instead of 桌子上面.
- 桌上 (dropping 子) is also natural, especially in writing or set phrases.
All mean “on (top of) the table/desk.”

Is 桌子 “table” or “desk”?

桌子 is a general word for a table/desk. Context disambiguates.
If you need to specify, you can say 书桌 (desk for study), 餐桌 (dining table), etc.

How do I negate this sentence?

For completed events (past-like), use 没(有) and drop 了:
- 我没(有)把电脑放在桌子上(面).
For habits/intentions/refusals, use 不:
- 我不把电脑放在桌子上 (I don’t/won’t put my computer on the desk [as a rule]).
To negate the resulting state:
- 电脑不在桌子上(了) (It’s not on the desk [anymore]).

How do I make this a yes–no question?

Does 把 require the object to be specific/known?

Yes—把 prefers objects that are definite/identifiable to speaker and listener.
我把电脑放在桌子上面了 is fine if it’s clear which computer you mean (e.g., yours).
Make it explicit if needed:
- 我把那台/我的电脑放在桌子上面了.
- Quantified is also okay: 我把一台电脑放在桌子上面了.

Do I need a measure word with 电脑?

Can I say 我把电脑在桌子上放了?

No. In a 把-sentence, the verb must immediately follow the object, then its complements:
- Correct: 我把电脑放在桌子上(面)(了).
Placing 在桌子上 before 放 breaks the required 把 + O + V + (complement) order.

How would I turn this into a command?

Simply drop 了 and (optionally) the subject:
- 把电脑放在桌子上(面)。 (Put the computer on the desk.)
You can add a softener like 吧:
- 把电脑放在桌子上(面)吧。

Can I use 将 instead of 把?

How do I say “already” here, and where does 已经 go?

What’s the difference between describing an action vs a state (with 着)?

Action (what you did): 我把电脑放在桌子上(面)了.
State (what it’s like now): 桌子上(面)放着一台电脑 (There is a computer placed on the desk).
The 着 sentence doesn’t say who put it there or when.

Any pronunciation notes?