No matter how active or passive, or how abstract or real, a verb "performs" some action. That's why verbs are characterized by tense and duration.
A gerund, on the other hand, is a kind of snapshot of that action in progress. In capturing an action in progress, a gerund borrows from a verb's progressive tense (a.k.a., its continuous tense) and turns it into an activity--something that can be discussed as a subject or object and modified. For these two simple reasons, all gerunds are nouns and all gerunds end in the same "-ing" ending that continuous verbs end in. Consider, for instance, the difference between the two following sentences:
In the first example, "runs" is clearly a verb. The emphasis is on the action of it in the simple present tense, and the sentence answers the question, "What does Charles do?" (Charles runs.) In he second example, however, "running" is a gerund. The emphasis is on the activity of it without tense, and the sentence answers the question, "On what does Charles insist?" (Charles insists on the activity of running.) The difference between them is simple: an action is performed in time and duration, whereas an activity is an idea without concern for time.
Modifying gerunds is tricky. (By the way, the phrase, "modifying gerunds," is a gerund phrase!) Because they're like verbs, sometimes a gerund is modified adverbially, just the way their root verbs would be: "Fastidiously farming one's crops takes patience" (or, as a verb, “When one farms fastidiously...”); "Farming without pesticides today takes a lost skill" (or, as a verb, “When one farms without pesticides...”). At other times, because a gerund is a noun, it can be modified adjectivally, the way nouns are: "Natural farming may be a lost art"; "Modern farming relies on a great deal on technology."
Just keep in mind that modifying a gerund can potentially answer, both, adjective-type questions such as, "What's it like?," and adverb-type questions such as, "How?" or "When?"
If you grasp the differences among verb types, then gerund types should be an easy lesson, because gerunds keep the same characteristics as the type of verb whence they came.
Furthermore, when gerunds take predicate objects and modifiers, no matter how complicated the results may seem,that whole collection of words and phrases bound to that one gerund is, in fact, a single gerund phrase: