Library databases look for the exact words that are typed into the search box: other forms of these words are not found. To include various word endings in your search, you can use truncation, a powerful search technique that allows you to broaden your search.
To truncate something is to cut it off. In the context of searching it's cutting of a word and placing the truncation symbol (*) at the end. The database will then return results that include any number of characters (including zero) after the cut-off word -- which is called the 'root word'. Root words must consist of 3 characters at a minimum.
So, if you search on the root word:
you'll retrieve child, child's, children, children's, childhood.
will retrieve invest, investor, invested, investing, investment.
A wildcard usually replaces zero to one letters inside the word or at the end of the word. Wildcards are useful for retrieving alternate spellings (i.e. British vs. American English) and plurals. The question mark (?) is often used as wildcard symbol.
will retrieve labor, labour.
will retrieve woman, women.
will retrieve leader, leaders but not leadership.
Not all databases use the * and ? symbols, so check the help screens for details of the symbols recognized by the database you are searching.