Your resource pool regenerates every turn up to your current limit, which is based on how many scrolls you have sacrificed from your hand. For instance, if you have sacrificed 3 scrolls for growth resources, you will be brought to 3/3 growth at the beginning of every turn. Also, whenever you sacrifice a scroll to raise this limit, you are given a resource. Ex: 1/1 becomes 2/2. However, you can only sacrifice one scroll each turn.
Other methods of gaining resources involve the use of memorials. They increase the resource limit by one, but do not provide any resource the turn they come into play.