There are many different kinds of resources to use in Marvel Future Fight.
Energy[]
This is needed to enter missions, to gain other resources. It recharges overtime.
Crystals[]
Crystals are the premium currency in the game. 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.
Biometrics[]
These are needed to obtain new characters, and rank up existing ones. They can be obtained in special missions and through Dimension Shifts, Shadowland, as well as many other game modes.
Materials[]
Typically used in leveling up character equipment. These include Dimension Debris, Black Antimatter, Norn Stones, Stark brand 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).
Strategy re "Tier 3 materials" and beating World Boss Legend[]
(Particularly as a relatively new player) It's important to identify which materials are for which tier and for which characters. Cosmic Cube Fragments, Essence of Dimension, and Titan Component Packs are used to progress characters to Tier 3. Cosmic Cube Fragments (yes, again), Awakening Crystals, and Mandalay Gem Fragments are used to Awaken Potential. A character can either go to Tier 3, or Transcend their Potential, or neither. Characters that can do neither can't be on the main team in World Boss Legend, the content providing the best rewards in the game, so care should be taken with how these 5 materials (collectively referred to as "Tier 3 materials") are used, and to acquire them voraciously.
- Note that World Boss Legend is difficult, so your expenditure of the above resources should focus on creating a main team of three (3 being required) for it. That team should include at least one character that reputedly massacres one of the World Boss Legend fights, and the other two should probably include either support/lead characters like Cyclops or Star-Lord (mentioned because they're the easiest to get) that can support your choice of damage dealer, or fundamentally strong characters that are useful for all content (e.g. Beta Ray Bill, who is acquired while progressing Star-Lord through his Epic Quest).
- Warning: This strategy is not meant to imply a mad dash toward WBL, as World Boss Legend is so difficult that, if you unlock it too soon, you may find yourself unable to beat it. This will incur other costs, as it will dilute the number of times you can beat World Boss of the Day.
Cover Pieces[]
Cover Pieces can most commonly be found in Dimension Rifts. These can be put together to obtain rewards and bonuses.
Custom Gear[]
Custom Gear can be equipped to heroes, adding varying bonuses. They are found in Special Missions, Chaos Chests, and the in-game store.