WorldCat does not appear to have an end-user training site. However, you can navigate to extensive help. From the main entry screen, click on the help button as illustrated below.
|Truncator||Wildcard||Exact Phrase||Other Tips|
# for a single character
Plurals - add a + sign to the singular form if the plural is formed with either s or es
|To search for the plural of words that change form, such as mouse or story, search for both forms and combine them with OR|
|From the advanced search screen, click on Help for search tips|