Gerund phrases function like nouns and can serve as subjects, direct objects, predicate nominatives, and objects of prepositions in sentences. Examples include "Tracing the history of hockey is fascinating" where the gerund phrase "Tracing the history of hockey" is the subject, and "The early history of hockey intertwined with the history of skating on ice" where the gerund phrase "the history of skating on ice" is the object of the preposition "with". It is important not to confuse an introductory participial phrase with a gerund phrase serving as the subject, as in the sentences "Playing hockey is fun" versus "Playing hockey, they had fun".