That's like stating I wan to fly a plane. How do I do it. Answer, get in
the cockpit and start operating the controls.
You could start by looking at Word Helpf for "Formula" and then maybe
=(Formula) field.
Basic example. One row x 3 column table. A1 = 1 B1 = 2 in C1 put
{=(a1+b1)} where the { } is field code delimiters the pair is inserted
using CTRL+F9