At this late stage one has to wonder if there can be any worthwhile material by or about Feynman that hasn't already been published - the answer is, in this case, yes - but this doesn't offer a tremendous amount that would be new to dedicated Feynman fans. It's really for completests and neither a great nor terrible place to start for newcomers.
For just such newbies to Feynman I will briefly disclose that he was a Nobel Prize winning theoretical physicist who worked on the Manhattan Project in his youth and became famous not only for his professional skill but his quirky and irreverent public persona and his capabilities as an educator, both of the general public and of student physicists.
This lecture was omitted from the famous three volumes of lectures based on a two year undergrad introductory course that Feynman taught at Caltech. It is a demonstration of the fact that planets orbit the sun in elipses if Newton's Law of Gravitation is correct and perturbations from all the other planets are ignored - using only plane geometry. Since only a few diagrams and notes from the lecture remained, along with a voice recording of it, it was quite a task to reconstruct the proof, which, as is pointed out by Feynman himself, whilst elementary, is not simple. That said, the explanation of the demonstration could not be clearer and anybody who can follow school level geometry will be fine. Because there are a large number of diagrams, what appears to be a lengthy (and therefore possibly intimidating) wodge of physics is in fact something you could read and understand in a couple of hours easily.
Additionally to the reconstruction and explanation of the proof, there is a mini-biography of Feynman which is best (as always) when telling anecdotes, not history, a transcript of Feynman delivering the lecture and a brief history of the relevant discoveries about the nature of the solar system, gravity and the way things move.