Tech Centers have upgrades which may be researched along the game
Upgrades may be global (available for all target unit types at once) or per-unit
Upgrades researched in the Tech Center are always Global
Per-unit upgrades usually require a certain Tier to be reached in the Tech Center first
Upgrades may unlock abilities on units (eg.: capture, resurrect) or provide some specific effect, like speeding up Morphs
Per-unit Weapon upgrades are also called “abilities”, like the Samson’s Fire Rain. To use it once researched, first click “D” then right-click on the unit or ground target.