To gather needs:
The sponsor will give you his or her interpretation of the needs. The sponsor might also give you the names of other people to interview. You can interview the sponsor and other people, or you can use requirements-gathering tools, such as brainstorming, the nominal group technique, focus groups, workshops, and affinity diagrams.
Use structured, unstructured, or semi-structured interviews to identify needs. The interview process involves identifying each participant, and asking a series of questions based on that person's role in the project.
First, you might need to explain to the sponsor and project staff what you are doing, such as gathering needs, categorizing them, and establishing the requirements baseline. You might also need to explain how that baseline is the basis for the project plans that you will develop.