How do I get rare earth I can't steal any cause I can't win any challenge battles?

You need to gather the rare earth. if you are a low level stick to the Level 1 field where you cannot be stolen from. Until you have VIP level 7 you will need to find a location to gather manually. Tap the field number at the bottom and type in a high number to move to a field near the end and move around until you find an empty spot.

As you get stronger you can move up levels to gather more and if you can reach VIP 7 then you will be able to use the Auto occupy option to find a spot for you. Remember that gathering in fields above level 1 though is open for others to steal from you.