Technology is used to increase the capacity of buildings, reduce the cost to upgrade buildings, increase the strength of your troops, and so on. Technology must be researched before its effects are applied to your empire.
To research a technology, you must first acquire the required resources in your empire's inventory, then click on the Learn button next to the desired technology you would like to learn.
Empires may only select a limited number of technologies to research at a time. At the start of the game, this is limited to 1 technology at a time.
Once the learning process has started, you will need to wait a certain amount of time before the research is complete.
Once an empire has learned a technology, they will retain that knowledge even if they lose all their nations and are forced to start over.