A Params List can look like this

AuthorId
SortOrder

Default Values help in cases where the query is usually used without setting params first, or if most params will remain the same. Then you can change it to this:

AuthorId=42
SortOrder=Asc

Default Values can use Tokens to get values from the context like URL Params. So this is valid too:

AuthorId=[QueryString:Author]
SortOrder=[QueryString:Sort]

You may also want to set defaults in case the context doesn't have params. Like this:

AuthorId=[QueryString:Author||42]
SortOrder=[QueryString:Sort||Asc]

Last but not least you can also stack the tokens to try one or another, like this:

AuthorId=[QueryString:Author||[App:Settings:DefaultAuthor||42]]
SortOrder=[QueryString:Sort||[App:Settings:DefaultSort||Asc]]

just try it 😉