Gerunds are verb forms ending in "-ing" that function as nouns. They can be subjects, objects, or objects of prepositions. To form gerunds, add "-ing" to the base form of the verb. Examples of gerunds used as subjects include "dancing is fun" and "cooking is my hobby." Gerunds can also be objects, such as "I enjoy learning English" or "he does boxing in the gym." Prepositions can also take gerund objects, like "my love for reading."