|- how much minerals one gets: Number of mines multiplied with the "density" of the material which varies from planet to planet. You see denstiy on planets without mines directly in the brackets, for those with mines you have to go to the "build mines" to see it. On PC, you also see denstiy when hovering the mouse over the planet on the starmap.|
-what do the numbers mean next to the minerals: first number is how much of the mineral you have mined and available on the planet. Then how much is left in the ground (like density, varies from planet to planet). Then, if there are no mines you see XX%, which is the density. Otherwise you see +xx, which is how much you mine each turn.
All in all it is quite a complex game. Best you take some time experienting in single player games and reading the documentation. In spite of all simplifications here at Nu to make beginner games more easy, at it core it is a very oldschool game, which means a very steep learning curve. Good luck!