Searches on the Hub deal only with these things: title, summary, keywords, publisher and/or author.
Search queries are divided into terms and operators.
Terms come in two types: Single Terms and Phrases.
‘Boolean’ operators ('OR' and 'AND') allow several terms to be combined, to form a more complex query.
You must enter them using capital letters (eg, 'OR', not 'or' and 'AND', not 'and').
"service management" leadership "service management" OR leadership
The AND operator matches items where both terms exist in their title, summary, keywords, and listed publisher and/or author. For example, the following will start a search for things on the Hub that contain "assessment" as well as "rating":
"assessment" AND "rating"