2) Can also be used as "all right" in some cases (usually while coming to a mutual agreement).
3) Pronunciation: the Y is said like any other Y. the two A's are pronounced like the letter 'U' in the word "Blunt". The L's are prolonged and are said by placing the tip of the tongue on the middle of the roof of your mouth (Like the French 'L').
2) Yalla bye.
1. Ya which is like a preposition usually used to call someone else.
2. Allah, which means God.
Actually, yalla has too many usages like acceptannce, confirmation, urgency and many other meanings.
Yalla jayi : I am coming
Yalla wlow : Hurry up
and so on...