why there are 2 different classes one for fields & another for entity itself It seems like fields class is used for predicate search. Is that correct

Because LLBLGen Pro uses an object /class (EntityField) to map a database field. (Object Oriented Design)

An EntityField holds many properties other than value, and have some operations/methods which change its state or modify these properties.

Please check the properties and methods of the EntityField class in the LLBLGen Pro Reference manual.