Jobs that appear here are created by the office with the expectation that professionals will apply to them. When you apply, you will be asked to submit a short explanation of why you are qualified for the role and potentially upload your resume. Once you apply, the system will create a new message between you and the office in your Messages tab. Any subsequent communication about the job will take place in Messages.
If the job is a temporary one, you may receive a request from the office via the bookings tab. If they don’t send you a booking request and they just offer it via a message, you may want to create a proposal to them so that it’s an official booking.