Firstly you need wood for a pickaxe. Next you'll need to mine down at an angle until you get to stone, Use this stone to create a furnace (8 Cobblestone. Found in the crafting table menu). Now you want to mine into your mine until you find a version of stone with pink pixel on it. This is Iron which can only be mined with a stone pickaxe

Now to smelt the Iron you need either Coal, Charcoal or logs. If you found coal while looking for Iron put it on the bottom section of the furnace, if not then Charcoal can be made by smelting wooden logs with wooden logs or to completely bypass that section just smelt the iron with the logs.

If you need any help feel free to PM me.