I live in Brazil and we have many coconut trees here on our 8 acres. Firstly there are two types. The green ones which you see in a beach bar with a straw in them.
The older type you see available in stores.
I am assuming you are referring to the older type with the white coconut meat inside. The ones in the store will already have the outer husk removed. The hard shell can be opened using the back of a heavy knife. Here they use a machete. They tap it, rotate it, tap it, rotate, tap until they have made a circle and it opens. They do this horizontally.