This game is sort of a hybrid of tower defense + real-time strategy. Have you played any of these types of games?
You have four workers who can morph between different roles, whose descriptions show when you hover your mouse over them in the top-left. Type 1 is the Defender, the only one who can attack enemies, for example.
Use the workers to harvest as many resources as possible across the planet. Have them attack enemies, heal each other, and build turrets/repair the ship as needed. Don't lose your ship and try to not let anyone die. Build one turret next to your ship per (threat level - 1). Then at the system map, use the resources you gathered to upgrade your stuff.