There's nothing (there)

This phrase means "nothing is (there)". It's used to describe a situation that is uninteresting and uneventful.

This phrase can be used with the word "there":

I answered the door when I heard the knock, but there was no one there.

Or it can be used with a phrase that indicates where you're talking about:

There's no one at work except me.

You can use the word "happening" to say that there are no interesting situations or events:

There's not much happening right now, so I think I'll take a break.

Using "there is" is good when you're describing a general situation, rather than a specific person or thing. If you want to be more specific about the person or thing, use "___ is ___":

No one is at work except me.

(a TV show) is on

This is a verb used to discuss TV shows. A TV show is "on" if it is playing right now.