Let's say, for example, you're researching the keyword "how to start a blog" for an article you want to create. "Blog" can mean a blog post or the blog website itself, and what a searcher's intent is behind that keyword will influence the direction of your article. Does the searcher want to learn how to start an individual blog post? Or do they want to know how to actually launch a website domain for the purposes of blogging? If your content strategy is only targeting people interested in the latter, you'll need to make sure of the keyword's intent before committing to it.
The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.