How do you earn metals?

You earn metals by visiting your friends’ planets (to find your friends’ planets select ‘Galaxy’ while on your home planet from the icons on the left), you can tell when there are metals available as the metal dispenser will be glowing. The metal dispenser (when not glowing) looks something like:

You can only collect metals from each friend once per GMT day, so once you’ve collected metals from a friend, you need to wait until after the next midnight GMT before you can collect more metals!