You're changing the channels on the TV and looking for something to watch, but nothing looks interesting. You say:
There's nothing good on right now.
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.
This is a verb used to discuss TV shows. A TV show is "on" if it is playing right now.
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