You can also go inside the store to purchase more supplies. Once you reach the surface again all you need to do is walk by the general store and you will automatically sell all of your precious ores and gems that you have gathered. For example, if you come across weak ground you will need to use a support and if you dig downward you will need to use your ladders in order to get back out. Your mine cart hold supplies that you will need to make sure that you do not get stuck down there and that you can get back out of there.
To get to the mines you need to go to the elevator to get down there and dig to gather the precious ores and gems. The tutorial tells you the object of the game which is to gather as many precious ores and gems as you can and sell them in the shop. Once you select your level of difficulty you will be asked if you want to take the tutorial. There are 3 levels of difficulty Easy, Medium and Hard.
The Gem Miner: Dig Deeper Android App by Phil Symonds is a game for the Android.