How use a gerund as noun?

A gerund is the present participle (the -ing form) of a verb.

A gerund is used the same as a noun, as the subject of a sentence or a clause, and as the object of a verb or a preposition.

Examples:

Dancing helps keep me in shape. (subject of the sentence)

The exercise that dancing provides keeps me fit. (subject of the relative clause)

I began dancing at the age of six. (direct object of the verb 'began')

I always make time for dancing. (object of the preposition 'for')