A verbal is a word made from a verb but which functions as a different part of speech in a sentence. Participles, gerunds, and infinitives are all verbals.
A gerund is a verbal formed by adding -ing to the root form of a verb. It functions as a noun. Like a noun, a gerund can be the subject of the sentence, the direct object of a verb, or the object of a preposition.
Gerund as subject: Doing homework is not fun.
Gerund as direct object: I don't like doing homework.
Gerund as object of a preposition: Many students are against doing homework.
In these examples, the gerund "doing" is followed by its object, "homework." This is called a gerund phrase.
In this video, Paul explains about gerunds.