There are many different kinds of resources to use in Marvel Future Fight.
This is needed to enter missions, to gain other resources. It recharges overtime.
Crystals are used for various reasons. They can be used to purchase uniforms, biometrics, gold, and stuff from the store. They are earned in the daily achievement, the check-in reward, being mvp in alliance battle, in-app purchases, timeline battle, and special events.
These are needed to obtain new characters, and rank up existing ones. They can be obtained in special missions and through Dimension Shifts, as well as many other methods.
Typically used in leveling up character equipment. These include dimension debris, black antimatter, norn stones, stark brande blueprints, and some others as well. Found in story missions, dimension rifts, world boss, the stores (both of them), and the converter can now change the type of norn stones you have (excluding chaos stones).
Cover Pieces can most commonly be found in Dimension Rifts. These can be put together to obtain rewards and bonuses.