Salam.
Okay, so here is the actual dua. "Allahumma atina fid-dunya Hasana, wa fil-akhirati hasana, waqina adhaba an-naar" which means "O our Rubb! give us in this world that which is good and in the Hereafter that which is good, and save us from the punishment of the Fire"
However, at the end of that du'a, some people add "waqina adhaba qabr, waqina adhaba hashr, waqina adhaba meezan" - which basically says "and save us from the punishment of the grave, the punishment of the [day of] gathering, and the punished of the scale (meaning, hypothetical scale used to measure good deeds against bad deeds on the day of judgement)" - I think it's an innovation though. I have yet to come across a hadith about that. But I could be wrong, so Allahu A'alm. salam
"Muslimeena fil Kuli makaan" basically means "Muslims everywhere" - so it's usually said when a dua is made, and it's basically for all of the entire Muslim Ummah.