In Sins of a Solar Empire II, you become the ruler of an advanced space faring civilization that has been in a state of war for the past 35 years. There are three races, and two sub-factions for each, that you can choose to control. Each of the races/factions below have their own unique play styles.
In order of increasing gameplay complexity, we have:
TEC - A human civilization with strong economic capabilities. Before the war, they were peaceful traders.
Loyalists - Specializes in defensive play, preferrable to be isolationists.
Rebels - Specializes in offensive play and desires to eradicate aliens and impure humans (Advent).
Vasari - A highly advanced alien civilization that’s been fleeing across the galaxy for the past 10,000 years.
Alliance - A faction that prefers to work in conjunction with other players.
Exodus - A faction that seeks to destroy anyone who gets in their way.
Advent - An advanced human civilization that has embraced the use of cybernetics and psionics.
Loyalists - They seek to forcefully convert the galaxy to their fanatical cause.
Rebels - They see corruption within their Loyalist brethren and seek to purge it.
Goal
As ruler, your goal is to explore the surrounding galaxy, expand to new worlds, exploit the resources you find on those new worlds, and to exterminate your opponents.
Go over the basic 4X elements.