What is the difference between finish and finished?

The past participle (“finished”) here either functions as an adjective that modifies the noun “action” in this sentence or it is part of the verb. The former feels right to me, but either way, “finished” is correct. The correct form is the past participle “finished”.

Is it grammatically correct to say “I finished my homework”?

People say “I finished my homework” all the time, but is not good grammar and your teacher would deduct you for it. For some reason, over time, conversational American English has dropped the “have” from the sentence, but if you want to be grammatically correct and use a shorter sentence at the same time, you should say “I’ve finished my homework”.

What is the past perfect tense of “I finished my homework?

(This sentence is in present perfect tense which shows the action that has completed at the time of speaking.) I finished my homework. (This sentence is in simple past tense which shows the action that was completed in the past.) People say “I finished my homework” all the time, but is not good grammar and your teacher would deduct you for it.

Is it correct to say that my home work is completed?

Since it is MY home work, it is redundant to mention that it is finished by myself. When we do not know who the agent is, or when it is very obvious, we do not mention the agent. Grammatically the sentence is not wrong. However, I would prefer to use: My home work is completed. Finish and complete almost mean the same.

When to use “when” and “have finished” in a sentence?

When you use the second phrase you should really mention when, to make it clear. ‘I finished my homework yesterday evening’. “Have finished” connects to the present more than “finished.” You typically could use the two forma interchangeably when talking about recent homework. Even the moment after you put down your pencil, the past simple is fine.