Question about numbered header styles

I am writing a book that will use numbered headers. I want to have a chapter number (1, 2, 3, 4), and subchapters organized by legal numbering (1.1, 1.2, 1.2.5, etc) where the first number represents the chapter, and the next represents the first level heading, and so forth. I want it to read like this:

Chapter 1: The greatest chapter ever

1.1 Starting the greatest chapter

1.2 Going further with the greatest chapter

1.2.1 Don't go too far

1.2.2 Go further

1.3 Going farther than farther

Chapter 2: The second greatest chapter

2.1 Starting the second greatest chapter

I am trying to use heading styles with levels, but I can’t get the numbering to work right. Can anyone explain how to do this?

Thank you.

– Greg

RFO