When you open up the calculator you'll see some fields on the left hand side that are blue.
They include Head weight, Tank Full, Tank Empty, Suit, BP, Light, Doubles?, and Weight Intergrated.
Apparently the head weight approx 8% of your body weight. You can do the math on that.
There is a table with the most common tank sizes on it, where it has the tank size and then full and empty. Air has mass so a full tank is going to weigh more than an empty tank. Steel tanks typically are very negatively buoyant when full and slightly negatively buoyant when empty. Aluminium tanks start off negative and then end up positive. Assume that you'll be diving an AL80. Fill in the buoyancy for that.
DR SS plates are around -5#. Pop that in there.
Assume a non-canister light is going to run our -2#'s.
You're not diving doubles so enter '0'.
You're not diving Weight Intergrated, so again '0'.
If you go to the websites of various wetsuit manufactures, you can typically find the buoyancy characteristics of various wetsuits. Input the info you find.
The spread sheet will then tell you the amount of lift you need in Red.
Seriously, update more of your profile and describe where you see yourself diving.