The demo is empty. It needs some motivation to keep people there. For example other games have coins that you can collect (moving coins? gold meteorites?), or even a few npc like an ufo would add some objective while waiting other players.

what can I do with the oney? Can I buy amomo or health? How?

It's very difficult to navigate spaceships. I made a somewhat similar game with only one star a long time ago so I remember some tricks fot I had to play a few miutes before my fingers got rememebered the tricks. I'm not sure if it's a good idea, but it would be nice to show the currrent trajectory and the trajectory if I continue to press the forward button as dotted lines.