Here is a list of all things Flattiverse offers. This includes units and also elements.
Plasma is used to build torpedos and drive shields. Plasma will be consumed when building torpedos or when shields get hit. You can build a Torpedo out of 100 plasma pieces of any level. You can convert 2 plasma pieces to one plasma piece of the next higher level.
Plasma can be refined by a component on a ship or it can be found in a more refined form in the corona of a sun (if the sun has such a corona). Each refinement doubles the power of the plasma. There are six levels of refinement. Therefore level 6 is 64 times as strong as level 1.
If you want some design guidelines: Draw the various levels of plasma in those colors: