Is the translation for "Güzel gün" : "beautiful day"?

and does "Bugün güzel" mean "today is beautiful"

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Does "O" stand for she/he/it is 

or just she/he/it, without is?

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Does "bu" stand for this is or just this?

When is it "this is" and what does bular mean?

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Teşekkürler

Hopefully a native speaker can help but here is my shot.

Yes "Güzel gün" is "beautiful day" and "Bugün güzel" is "today is beautiful"

"O" is she/he/it.

"bu" is this and "bunlar" is these.

Believe it or not, there is no verb "to be" in Turkish. There used to be but it is obolete! Here is a link that discusses this: http://www.turkishclass.com/turkish_lesson_67