Each section of How to Design Programs has a "Next" pointer, a hot-link to the next section. Most sections also have a hot-link to a corresponding section of the DrScheme Companion, which gives more specific information on how to use the DrScheme platform. In its current form, the "DrScheme Companion" does not have links back to the regular textbook, so you'll need to use the "Back" button on your browser.
I recommend that you read this stuff on-line, with DrScheme running at the same time, so that every time you read something you can immediately switch windows and try it. If you want to try some Scheme at home, you're welcome to download it for free.
The Preface is optional.
Please start at Computer Programs, Information, and Data and follow the "Next" links (and the corresponding sections in the DrScheme Companion) until you get to the section entitled Conditional Expressions and Programs, which is where we'll start the next day.
Along the way, I recommend (but do not require) that you try the exercises in the text; at this stage, they should take only a minute or two apiece.