"I get it", "I got it", "I understood" is there a real difference between these ways of speaking? What's the difference between them? In what cases should we use one or another of them in speech and writing?

Correct the sentences below, please, if I've done any mistakes I won't be here for a couple of hours. I'll get back as I finish my job.

Can I say some same sentences both in Past Simple and Present Prefect Is it true that quite often the same sentence can be said in Past Simple and in Present Perfect and its meaning won't change a lot? P.S. If you found any grammar mistakes in my question, please, let me know about them.

In what cases is "would" used? In what cases is "would" used and when is it used instead of "will"? Thank you in advance

When you listen to music, are you interested in a song's lyrics? What is more important for you, how the song sounds or what is sung in the song about? Does the song's lyrics have a big influence on you when you listen to it, or it doesn't have a lot of matter and you just enjoy how the song sounds?

Is it okay to use the constraction of "have" and "has" in formal speech and writing For example: "I've just finished my work" "He's arrived" "I've been waiting for you" "She's not seen me for a long time" "I've been working hard studying English for the last five years"

Question to people who learn Russian. What Russian authors and poems do you know? What classic authors do you know? What compositions have you read and what of them do you like or dislike and why?

In what cases is the word "were" used instead of "was" when subject of speech is "I"? The question is about the past tense of course. Hope you understand what I mean. Thank you in advance.