As you progress your Hogwarts adventure you were periodically meet new friends.  Each friend has 10 friendship ranks which can be leveled up by completing quests, sharing a meal together, playing a game of gobstones, and enjoying some butterbeer.  Each activity is essentially a series of 4 questions that you must answer to gain progressively more friendship points.  After each level up you will be rewarded a small amount of gems (Real Money Currency) or energy.  Each friendship guide linked below will contain detailed information and the answers to every question friends will ask during activities: