What do you think about using other tunes in your own song?? Is that done in today's music?

No...it's the same as if you plagiarized an essay. You need the person who wrote or owns the songs permission to use any of it in your own music. There have been lawsuits over using just a few notes of a song that sounded as if they belonged to someone else.

Yes it's called sampling

This exact same question was already asked by someone a couple of days ago. Do you have the same class as this person? You really need to do your own research and form your own opinions if you expect to learn anything!

I don't really care for it, however, it has to be a damn good song to make it work the second time. Just look at so many ofthe remixes and most of them suck. So unless you want to try to live up to the original than I suggest not doing it.

It is perfectly fine so long as you obtain permission from the copywrite holder.

Creatively speaking, musicians from the danw of time have done this.

If you choose to use someone elses tune, all you need to do is make it your own (that's if your the musician). If you play guitar or piano or whatever you have and you have a piece of music, no one controls the way you play the music but you and then you'll find it easier to create your own melodies and riffs.