Absolutely, you can decide to get paid for answering questions. You define the rate you want to receive per questions in the Setting tabs under "Rate per text & question" and every time you receive a premium question, you get paid when you answer it. You see when you get paid for a question if you see a $ sign above the answer. When none appear, you are providing your answer for free.
Premium questions are all the questions you receive from people you are not connected with or that you have removed from your free list. If someone has already your contact information in their phonebook, they can send you question for free by default as they could do the same via regular text. You can change this at anytime in the Settings tab, navigating to Contacts and then to Free.