Star Trek was one of the earliest computer games, and this is yet another version of it but with so-called 3D action. The idea is to defend an 8x8 galaxy against attack from an alien invasion fleet, with yours being the only ship.
You start by examining the sectors around your ship with the long range scanners. Every time you do this, it updates the galactic map accordingly. Having found an enemy sector, you can warp to it using the navigation computer where a red alert will sound and alien ships move across your view one at a time while you try and hit them using a cursor.
Having cleared the sector you move on to another until the galaxy is cleared or you are destroyed. You have two gauges for energy and shield strength and these are reduced by enemy hits and have to be replenished by making a lunar lander-style landing on a planet.
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P. It's very nostalgic and brought back happy memories.