The authors begin by exploring the basics of space -- its characteristics, orbits and gravity, and so forth -- and continue on to spaceships, space stations, and space colonies. Next comes a chapter concerning the Sun and the planets: how they were formed, the atmospheric and geologic characteristics of the planets, and how terraforming might be accomplished.
Chapter Four deals with designing a starship, faster-than-light travel (the authors say travelling close to the speed of light is highly improbable, but there are ways of handling the problem), generation ships, and more. There's an introduction to the Milky Way, information on supernovae, neutron stars, and black holes, and how to design a planet.
Next, the authors cover aliens and possibilities for galactic civilisations, including empires, republics, and federations. Molecular technology and virtual reality are also discussed, as well as time travel, invisibility (as yet no one has come up with an entirely convincing way to make something or someone completely invisible), androids, cloning, and genetic engineering. The book closes with a chapter on alternate histories and parallel universes. There's a bibliography at the end.
The books Writer's Digest has on writing science fiction are excellent. This one is a good overview of the many things a science fiction writer may want to know.
If you like this one, try: How to Write Science Fiction and Fantasy by Orson Scott Card, Space Travel: A Writer's Guide to the Science of Interplanetary and Interstellar Travel by Ben Bova with Anthony R. Lewis, World-Building: A Writer's Guide to Constructing Star Systems and Life-Supporting Planets by Stephen L. Gillett, and Aliens and Alien Societies: A Writer's Guide to Creating Extraterrestrial Life-Forms by Stanley Schmidt.