What exactly different in these sentences?

Hi.

Carter Lee Hi.I have just some question about the following things.

1.I have finished my home work in 2 o'clock. You cannot use definite with present perfect.

2.I finished my work as at 2 o'clock.

Thanks a lot,
But i have question about your answers.
At 3, you use preposition like with.
But should i don't use preposition like this "i was finished home work".

P.S. When i saw my question, i just felt that are some weired.

hrsaneiHi. Carter Lee Hi.I have just some question about the following things.1.I have finished my home work in at 2 o'clock. You cannot use definite time with present perfect. 2.I finished my work as at 2 o'clock. Note the right preposition. 3. I was fin

In your third sentence, "finished" is more like an adjective than verb, therefore, it cannot take a direct object and you need a preposition to related it to "homework" .
Meanwhile, "homework" should be attached.
Hamid

Thanks Harmid,
This is off -topic, but actually i have felt hardness as bilanguage user about above that. Because when i talking to somebody, i can't think/use right away about such as your recommend.

So what is the best way? Actually as bilanguage user, it hardly overcome problems.

You need to practice all aspects of English. Expose yourself to extensive reading and listening and try to speak and write in English as often you can. Proficiency does not happen over night.
Good luck
Hamid