Stargus is a Starcraft Mod that allows you to play Starcraft with the Stratagus engine, as opposed to play it with the original Starcraft one. So unless you have a legal copy of Starcraft, Stargus will be pretty useless to you, since it doesn’t come with any graphics or sounds itself.
So why play Starcraft with the Stratagus engine instead of the original Starcraft one? There are numerous reasons. It allows you to play Starcraft under Linux and other operating systems not supported by the original Starcraft engine. Also the Stratagus engine allows you to tweak numerous parameters so you can play around with different unit strength and such.
Since Stargus uses a different engine, the game will not be an exact replica of the original Starcraft. If you want the original unchanged Starcraft experience, you will still have to run the original game.
Stargus is not an official Blizzard product, it’s a Starcraft modification, by Starcraft fans for Starcraft fans. You need a copy of the original Starcraft version to make use of Stargus. Starcraft is a registered trademark of Blizzard Entertainment.