Here are some instructions for you, they are in the game too.
Left/Right - Rotates your ship
Up/Down - Moves your ship forwards and backwards
Space Bar - Fire your weapons
Z - Tractor beam
There will always be 3 missions available to you that appear to the left of the image of the girl. Training and Making Space are missions that remain the same, the mission inbetween these two is the series mission and changes as you progress. Whenever you finish a mission in the series you will get a mission code for quicker access to that mission when you play next time.
If you are running low on bullets or health, try shooting some asteroids, sometimes they leave behind health and ammo. Just run into them to collect them.
You can collect astronauts by holding them in your tractor beam for about a second.
There is a minimap at the bottom of the screen. You can see your enemies on this map in red. Depending what mission you are playing the white dots can represent health packs or astronauts.
In the options menu you can change volume settings or disable music and sfx by sliding them to 0. You can also change the default key configuration here if you don't like the default setup.
You can fire an object from your tractor beam by pressing the fire button while the object you want to fire is in your tractor beam. This is can help you in a later mission.