Someone has already explained the use of this particle, but since I can't find the relevant post, here is what Wikipedia says about it:

يَا • (yā)

vocative particle preceding a noun used in direct address; only rarely omitted in such contexts; occasionally translated as o or hey يا كندا!‎ yā kanadā! O Canada! يا كريم...‎ yā karīm... (Hey) Kareem, ... يا حبيبي!‎ yā ḥabībī Hey my love!

You use it every time you are speaking with someone and you call them by their name. It's a vocative particle.