The word syntax bothers a lot of people - including me, I might add! I find it slippery: it is difficult to pin down exactly what it means or can mean - an elusiveness confirmed when consulting The Shorter Oxford English Dictionary:
(A) The arrangement of words (in their appropriate forms) by which their connection and relation in a sentence are shown … Also, the constructional uses … characteristic of an author.
(B) The department of grammar which deals with the established usages of grammatical construction and the rules deduced therefrom.
There is a fundamental difference between the two definitions. The first limits syntax to matters of word-relationship and word-order - a significant issue, certainly, but much narrower than B, which almost makes syntax synonymous with grammar itself.
It is definition A that governs the material here. The two previous chapters have already dealt with much that definition B encompasses, and there is further such material in the next chapter. This one looks at how words operate in groups - in phrases, clauses and various types of sentence - and how you can best arrange them to ensure the meaning required.