Networking Events

Hi everyone! I recently started my new job. I've always heard/read that people tend to attend these "networking events". I was wondering -

1. How do they get to know about these events?
2. What happens at these events?
3. How do you actually network?

Since this group is about startups, and I am someone who will eventually start my own business, I really want your help to help grow my knowledge and contacts.

Thank you!