The general difference is if you think about paper format VERSUS electronic formats.

Let’s see:

On the internet

When saying that you found a product or some information online:

I found this book on the internet.

On a website

When you want to specify a particular website on the internet:

I found this book on the internet on a website about English prepositions.
I saw this on Amazon.

For all the social media networks

I read this on Facebook, Instagram, Twitter

When we talk about websites, newspapers, magazines and companies that also exist outside of the internet:

I read it on the New York Times website.
I bought it on Sephora’s website.

On a post on Facebook, Instagram and so on

When you need to describe the exact location where you found an article or post online:

I saw this in an article on Facebook (let’s discuss In below)

I found it on a Facebook post.

On my Ipad/computer/tablet

When you describe that you have information on your electronic equipment/device:

 I keep all my pictures on my Ipad.

It’s on my computer!

To watch/find something on Netflix/HBO

I watched the movie on HBO.
You can find the new show on Netflix.

On my blog

I wrote about healthy living on my blog.

On the radio

She was on the radio this morning.

Now, IN…

Think about all the paper formats

I read it IN:

• a book
• a magazine
• a journal
• my notebook
• a newspaper

BUT

On:

• an online magazine
• an online newspaper
• an online journal

Now take this quiz: