First time cookin dinner, need size help?

This is my first time making dinner for my family, i dont kno why i just figured makin meatloaf cud be easy and a cool experience. Anyway i would go on google to look at cooking directions but i am an ameture and it doesnt tell u what the serving size is. What i really want to ask is how much ground beef or turkey do i need to feed a family of 4-5. Also what ingredients should i get for a juicy nice meatloaf for 4-5 and cookin directions or a link wud be very appreciated