A clean URL is one of the few SEO elements a visitor actually reads before they click.
Favor Words Over Parameters
A URL built from readable words is easier to remember, share, and trust than one built from IDs and query strings.
Avoid Changing URLs Unnecessarily
Once a URL is indexed and earning traffic or links, changing it forces a redirect and a period of lost signal, so get the structure right early.
Use Hyphens, Not Underscores
Search engines treat hyphens as word separators and underscores as connectors, so hyphenated URLs are read correctly as multiple words.
Next step: Use the URL Encoder / Decoder to check how special characters in a URL will actually be interpreted.