You may want to review complex numbers first.
Adding and subtracting complex numbers is pretty easy. You just collect like terms. For example, suppose you have to subtract 3 − (−1 + i). Then the 3 and the −1 are like terms, so you can subtract them to give 4. The i doesn't combine with the others, since it has as i in it. So the answer is 4 − i.
If there was more than one imaginary term, then we would combine them, just like we combined the two real terms here.