The standard form for a complex number is a + bi, where i is the imaginary unit, . You do complex arithmetic (addition, subtraction, multiplication, division, and exponentiation) the same way as you do real number arithmetic. The imaginary unit, i, is located above the decimal point key (bottom row, middle key). Accordingly, press i to enter i.
(6-3i) + (4 + 2i) = 10-I