Diamond ore is a block and is effectively useless for crafting things, its only use is decorative.
Diamonds are an item that drop when you mine diamond ore with an iron (or diamond) pick.
- Mine diamond ore with an iron pick to get diamonds.
- Make a diamond pick and mine some obsidian with it.
- Make an enchanting table with obsidian and diamonds (and a book).
- Grind for several days for the random chance to get a Silk Touch pick.
- Mine diamond ore to get diamond ore blocks.
- Profit! (Except for the fact that diamond ore is useless.)
I hope that explains things.
