with money you can buy ship or increase size of the ship

you take money from planet by mining
  thus reduce wealth of the planet


poor planet are good for buying ship or upgrating ship
  but that increase wealth of the planet

rich planet are not favorable because the richer the
  planet is, the more expensive the expenditure is

so it is simple , you mine the planet
  and buy more ship...bigger ship
  you will maybe want to buy from one planet
  and mine another

  but there is some limitation....

  your ship need fuel to travel , fight or mine
  fuel are buyed on planet, you will want to buy
  your fuel on poor planet, hope it is not too far
  away.
  the amount of fuel you can carry is limited on the
  size of your ship and its remaining cargo

  and yes your money is on a ship, mean all ship have
  part you your money, then you cant mine with one
  and spend with another, ship must be adjacent to
  transfert money and/or fuel

other part of the mecanic

  fight
  space ship can engage battle
  the bigger the ship is, the stronger it attack
  the stronger it sheild againt damage
  
  bigger is your ship, more fuel is consume

last part of the mecanic

  travel
  you travel from planet to planet
  their is nothing like coordinate
  only zone with planet and distance between zone