HALBUKİ

What does "halbuki" mean?

Can you please use it in a couple of sentences?

Thanks.

Halbuki means but, however, whereas.

Niçin şarkı söylemiyorsun? Halbuki sesin çok güzel.

Why don´t you sing? Whereas your voice is so beautiful.

OYSA Kİ

What does "oysa ki" mean?

Can you please use it in a couple of sentences?

Thanks

To quote from my copy of ´Turkish Grammar´ by Geoffrey Lewis, page 213

Halbuki, oysa(ki) ´whereas´, ´though´.

These represent the backward not forward looking ´whereas´ or ´though´, even when they begin a sentence, in which case the correct translation is ´yet´ or ´but´.

Halk, çok defa softayı idealistle karıştırır. Oysaki softa, idealistin tam tesidir.

The people often confuse the bigot with the idealist. Yet the bigot is the exact opposite of the idealist.

Hamdi beyin, çocuklarına tek bir fiske bile vurduğu görülmemişti.

Hamdi bey had never been seen to strike his children even a single flick of the fingers. (lit = Hamdi Bey´s striking had never been seen.)

Oysa ki ikisi de oldum olası haşarıydılar.

Yet they both were very naughty for as long as I´ve known.* 

[*my translation for the final sentence, whereas the original was ´Yet both of them were pests and always had been´]

This link to a past discussion on conjunctions also might interest you, especially lazy42´s explanations