All three components should complement, not repeat one another.
You: Prepare a 1-2 minute lightning talk about your research. This should be a unique experience or insight in simple, easy-to-understand language. Also prepare to answer questions about your research.
Poster: The poster should outline your research with interesting commentary about what you learned along the way. It should be a balance of visuals and text.
Handout: Best practices for handouts - 1) The handout should be double-sided. 2) The front side of the paper should include a picture of the poster. 3) The back side of the paper should include a literature review, cited references, further information about the topic, and contact information.
Best reason to give a poster presentation - Learn to see your research through the lens of others. Ask new questions!
A poster session or poster presentation is the presentation of research by an individual or group for a class or academic/professional conference. At a conference, the work is usually peer reviewed.
A room is reserved for poster sessions where researchers accompany a poster illustrating their methods and outcomes. Presentations usually consist of affixing the research poster to a portable wall with the researcher in attendance answering questions. Each research project is presented on a conference schedule for a period ranging from 10 minutes to several hours.
Adapted from http://en.wikipedia.org/wiki/Poster_session