Gerunds are words that are formed with verbs but act as nouns. They’re very easy to spot, since every gerund is a verb with ing tacked to its tail. There are no exceptions to this rule. Like all things grammar, gerunds do take a tiny bit of detective work to spot. The problem here is that present participles also end with the letters ing. Besides being able to spot gerunds, you should be able to tell the difference between a gerund and a present participle.