Forum:Snipe hunter priority and waboku

if my oppoenent summons a snipe hunter and says priority then discards a card(is it a cost???)to activate itz effect to destroymy face down waboku, do i have to respond rite there or can i chain after he rolls the dice???

How do priority work??? I still do not understand it concept of it after reading it online here I am a noob GIVE ME MORE EXAMPLES!!!!!!!!