What word frequency actually tells you
Ranking the words in a piece of writing is an old SEO habit that has outlived its original purpose. Search engines no longer count keyword repetitions, and writing to hit a density target produces worse copy that ranks no better.
What the count is still good for is editing. Seeing that you used “essentially” eleven times, or that a supposedly wide-ranging article circles the same three nouns, is genuinely useful feedback. It also confirms at a glance whether a page is actually about the topic you intended.
Reading the numbers
Density is the word's share of all counted words after filtering. For a typical article, a main topic word landing somewhere between 0.5% and 2.5% is unremarkable. Much above that and the repetition is usually noticeable to a reader; much below it and the page may not be as focused as you think.
For overall length and reading time, use the word counter. To check a title or description against search result limits, use the meta tag generator.