Fly to the first planet, collect all 5 star pieces and you will reach the next planet. The only thing you need to be aware of is that some planets have black holes, so be careful not to fall into them, or you will die. It's not very easy to die in the game though. If you don't have any blood, you will get gold by stomping on enemies. The gold coins will add a level of blood to the uncle, and at the beginning, the uncle only has 3 levels of blood. I'm sure it will become more durable as the game progresses. Most of the monsters can be stepped on, but you need to be careful with your timing. In a room full of electric traps, step on all the switches and you will get your first star.
With the help of this star, Mario has his own base in the galaxy. The goddess reappears and explains the setup of the galaxy in detail. The more distant the galaxy, the more stars are needed to reach it. So the game is played in the galaxy, with the base as the centrepiece. Use the first star you get to travel to the first galaxy. Each galaxy has 3 levels, each with a star reward, which can be obtained in different ways.
There are different ways to get them, either by defeating bosses or by other means.