Enter the number of sockets you want of each color under "Desired Sockets". If you know the current colors in your item, you can enter them under "Current Sockets".
Under "Stat Requirements", please enter the STR, DEX, and INT requirements as displayed exactly on your item.
"NChr" will give you the probability of getting your desired colors after rolling that many chromatic orbs.
For advanced users, "X" is a hidden parameter of the model. I recommend the default of 12, but you can play around with it. Higher values would make rolling off-colors easier.