Download Battleships Forever
There are not too many real time strategy games based in space so Battleships Forever is a great game in its genre. Already from the beginning you might be overwhelmed by the huge amount of different ships you can choose from in order to start your journey throughout space.
You have access to a tutorial mission that you should play in order to find out exactly how the mechanics of the game work. You will also have access to a huge number of weapons that can even be customized on your ship in order to give you the best armored vehicle in the fleet.