Query package is situated in the Query\Engine\MySQL namespace. It contains classes with basic ObjectInterface, which has one method: prepare with no parameters. This method forms valid MySQL statement with ? placeholders. SingleValueInterface and MultiValueInterface extend ObjectInterface. First of them has method value with no parameters, second - values with no parameters too. These methods return single value or array of values in right order, which was used in formed MySQL statement (or part of it). All classes (except Builder and Builder\*) in Query\Engine\MySQL namespace extend last two interfaces.
All namespaces of query package are listed here. They contain classes, each of them is interpretation of any MySQL argument, operator, function, flag, clause or statement. Builder class combines all of them. With help of this class you can build the most frequently used MySQL statements. For nontrivial cases you can use combinations of other classes.