How would I add block variants like stone or dirt has?

I know that it has to do with block data which makes up the number after the block so
minecraft:stone 0 - is regular stone
minecraft:stone 1 - is granite
minecraft:stone 2 - is polished granite etc.

I am trying to make a variant for a block to use in the nether, and I eventually want to do a tutorial video on how to do this, but I don't know where to start in the code editor for the block I want to use, any help would be great thanks in advance.