Excluding a term: The reply to the following query includes documents containing the term user but not containing the term guide (or any term with the same stemmed form, for example, guides).
user -guide
Making a term mandatory: The reply to the following query includes documents containing both user guide and any term with the same stemmed form as installation (for example, installations):
"user guide" +installation
Making a term optional: The reply to the following query includes documents containing user guide, as well as documents containing simple (even if the documents do not contain user guide).
simple ?"user guide"