Greetings in casual conversation in English can sometimes be tricky because they don't always match with the greetings we learn in English language textbooks. Find out how to respond to the very common question, "What's up?"
Keep in mind that this will not be necessary for you to use on your TOEFL test, nor will the TOEFL test ask you this question. "What's up?" is too casual for the TOEFL. However, if you are taking university or high school classes with other native English speakers, you will find that this is a very common greeting.