First, you get his phone number. Then grab your phone and dial the number. OK, that was a joke to help you remember: you don't want to know *how* to call him or her (that's actually Spanish grammar!) but *what* to call him or her. Normally, the professor will tell you. If haven't met her (for example, you are emailing before the course begins) you should call her Dr. NAME or Professor NAME. Don't ever call a professor by a nickname, unless by that you mean Dan instead of Daniel (for example), and then only if the professor tells you to. It would be bad if everyone calls the professor Dr. Stench behind his back because he never takes a shower and you called him that to his face... Anyway, ask the professor what he or she prefers. Some are more formal than others.