A gerund (verb + ing) acts like a noun in a sentence.
Seeing is believing.
Running a marathon is not an easy thing to do.
Watching TV is sometimes harmful.
Eating is always fun.
My hobby is painting.
She loves babysitting her sister.
I like listening to music.
I wasted all my afternoon by taking a nap.
I am afraid of singing a song on a stage.
Often, a possessive noun or pronoun comes before a gerund.
I hope that you don’t mind my using your pen.
Don’t be mad about my leaving early.
I don’t want you misunderstanding.
You will be amazed by my writing.