Even if you feel that you already know the basic structure of a Bash command well, carefully looking at the structure of a typical command line and knowing the rules of string quoting can make it much clearer what's wrong when something doesn't behave as expected. We use single quotes to keep characters literal, and double quotes to safely perform expansion for variables and substitutions. Developing disciplined habits with quoting and understanding how Bash runs commands in sequence is helpful not just for scripting, but for interactive command line work as well.
Having learned the structure of a Bash command line, in the next chapter we'll apply it to learning some essential commands that will form the basis of many shell scripts.