Closing remarks are very similar to the concluding paragraph of an essay. I have included a good example - see related links. The opening paragraph introduces the topic. The closing remarks provide a concise summary of the points made in the talk. Frequently, in the closing remarks, is a statement of the next course of action. Some people use closing remarks to thanks sponsors and other researchers, but this can be done in the beginning of the talk. The closing remark may be what the audience will remember most about the talk. One or two short sentences at the end, with words very well chosen provide an effective closure to the talk.