I have to prepare the presentation about my previous research experience and postdoc research proposal for 20 minutes. I need some productive suggestion about what I should include, how big and how much specific it should be
It sounds like your presentation essentially divides into two sections: what you have already done and what you intend to do in the future. With regard to the first part, you can probably assume that most of the decision makers have read you CV but necessarily any of your other materials (articles etc.). Still, rather than summarizing individual publications, I would produce a "strategic summary" of your research goals and career directions so far, and then mention specific research projects in that context.
With regard to the second, point your goal is to demonstrate that you understand their program of research well enough to design a project that would fit within it. That proposal should also have two elements, one showing how the skills that you bring to their "lab" will be valuable to them, and the other showing how your own career will benefit from what you learn as a member of their lab. In my opinion, the best post-doc experiences occur when you have something new that you can contribute at the same time that you also acquire further skills.
Starting my day on a beautiful note after coming across this discussion. Thanks Prof. @David L Morgan, your comment have given me a hole lot of what I need to know.
You have already submitted your CV hence mentioning publications and research work (and responsibilities) within 1 or two slides will be a better idea. Also mention how your previous work will contribute to postdoc work. Focus on future work you want to do in a postdoc.