In Metal Fatigue, they are two kind of resources, MetaJoules and ManPower.
MetaJoules[]
Rimtech Hover Trucks harvesting MetaJoules from Lava
MetaJoules or MJ are the primary resource of the game. Everything that can be build or produced will cost a certain amount of MetaJoules. This resource can be collected from Lava sources by Hover Trucks or produced from light by Solar Panels. MetaJoules can be considered as energy, that is then converted into matter using the Matter converter. If there is not enough MetaJoules, the build progress will be paused, and will later be resumed once MetaJoules are available.
MetaJoules are stocked in Matter converters and in Energy banks, with a maximum of 2300 and 1000 MetaJoules per building, respectively. Maximum MetaJoules capacity can therefore be raised by building Energy banks, or Matter converters (but very pricy for this only purpose).
The current amount and total capacity of MetaJoules is displayed in the top left corner of the screen, right to the clock. It is also represented as a red bar.
ManPower[]
ManPower or MP is the second "resource" of the game. As his name said, it consists in the number of people available to do tasks, like building Combot parts in the Parts Factory, or driving a :vehicle like a Missile Car. Many buildings and every units need a certain amount of ManPower to work, reducing the number of avalaible ManPower for units or structure being build.
ManPower is simply raised by building Cryo Farms, each of these adding 40 MP to the total amount of ManPower.
If a unit is being produced but the ManPower has reached 0 or less (e.g. a Cryo Farm is destroyed), the unit won't be deployed, and will wait until there's enough MP.