Type a headline, get a slug you can drop straight into a permalink or a file name.
Accented letters are decomposed into a base letter plus its accent mark, the marks are discarded, and apostrophes are removed outright so don't becomes dont rather than don-t. Everything that is left and is not a letter or digit becomes your separator, repeated separators collapse into one, and any at the start or end are trimmed.
Hyphens, for web URLs. Google has long treated a hyphen as a word separator and an underscore as a joiner, so word-separated slugs are read as distinct words. Underscores are still handy for file names.
Short enough to read at a glance. Three to six meaningful words is typical; very long slugs get truncated in search results and are awkward to share.
Yes, it keeps whatever you type. Trimming filler words is an editorial choice, so it is left to you rather than done automatically.
Characters with no Latin equivalent are stripped, so Cyrillic or Chinese titles will not survive. For those, write the slug by hand in transliterated form.