Friendship Points (FP) are used in Regular Summons and Goddess Worship offerings. You can hold a maximum 
[9999] FP at once. Any FP received while at the maximum will be lost.
Summoning a card costs [100] FP per summon. Up to 10 cards can be summoned at once for up to 
[1000] FP.
How to obtain Friendship Points[]
Friendship points are generated when you assist or are assisted by any of your "Comrades" at the start of a battle. You and your comrade gain [50] FP per assist. You cannot assist a comrade at will - it occurs randomly.
You can gain [2] FP by greeting players when visiting random kingdoms, or when viewing archwitch rewards. Greeting a comrade grants you [10] FP instead. Players may be greeted once per day in this way.
Greeting other players encountered while advancing in campaigns grants you [50] FP. Players may be greeted an unlimited number of times in this way.
The most efficient way to gain FP is to add many comrades and "help" their resource generating facilities. This is done by visiting their kingdom and tapping on up to three FP balloons above a resource facility. Your comrade will receive more resources and experience when collecting from facilities "helped" in this way. [30] FP is earned for each resource facility helped, for up to [90] FP per comrade, per day.
You may also gain FP from login bonuses; the amount varies, but it is most commonly available as [500] FP. Some quests may also give FP in varying amounts.
To sum up, here is a list of things you can do to obtain FP.
Can be done once a day (most reliable source of FP):
- Greeting your comrades: [10] FP per comrade
- Helping three of your comrades' resource generating facilities: a total of [90] FP per comrade
Can be done indefinitely throughout a day:
- Assisting or being assisted by a comrade in battle: [50] FP per assist
- Greeting other players while advancing in campaigns: [50] FP per player
- Greeting random players: [2] FP per player
Other possible ways to obtain FP: Login Bonuses, Quests, Ranking Rewards