A typical Japanese sewing or pattern book usually starts with gorgeous pictures of cute models in the finished projects, sometimes followed by a summary of all the projects available in the book.
At the end of the pretty pictures, before you dive into the patterns+instructions per se, there is usually a page indicating size information and other general guidelines on how to use the patterns. The page is usually titled ” 作り方”, sometimes in English “How to Make”
The rest of the text above the size chart are general pointers that are relevant to all the projects in the book. In this particular book it is giving information about the sizes that are provided for in the pattern sheet, and special notes for making the individual garments such as blouses/skirts/hats.
Because this content differs from book to book, I will not delve into the actual details of this particular passage. It is more important to know the terms for the body parts mentioned in the size chart so that you can at least know what measurements to take and what size to make. Also, from the size chart you can see that this book covers patterns for heights from 100-140, in 10 cm increments which means for each pattern there are 5 different sizes.
Important point to note, that the Japanese books use centimetres and meters instead of inches.
The pattern books are usually published for a range of sizes, usually in cm for children based on their height, and S,M,L for adults. For children, they sometimes give an estimate of the ages of the child and the corresponding size to make, but do take note that these are Japanese averages, so it is probably better to measure your child’s height/chest measurements and use the corresponding size on the table rather than depending on the age value.
For a list of frequently used terms in Japanese sewing books, refer to this page – Dictionary of Japanese Sewing Terms