sewing a zipper in a pillow

hi newbie here,never put a zipper in anything,wanted to know if someone could help me figure it out? i have a panel for a pillow that has a fold and i wanted to put a zipper in it so i could wash it when it got dirty but dont know how to put a zipper in.do i need to cut it where the fold is or leave it one piece? and then how to put the zipper in? if you need pics of the piece i am talking about i can send plmk and thxs so much for helping.
p.s. i got my daughters cow quilt done but cant post any pics until after christmas because i dont want her to see it lol so now i have to make the pillow to go with it.it isent a reuglar size pillow it is like a throw pillow thxs again

p.s.s. would love to know how to put a zipper in a pair of blue jeans too heheheheh