It's very simple theory, but effective when it comes to content marketing and SEO especially when you don't know what to do with your keywords.
Shareable content is the content which you write for the whole purpose of getting a lot of shares, likes, tweets, pins and upvote that indirectly increases the ranking of your site.
Linkable content is the content which you write for the whole purpose of getting a backlink. Statistics type of content is the linkable content. If you've written a research paper, you've observed you give a reference to the site that has some statistics facts.
The main difference between shareable content and linkable content is the duration in which they exist on the internet.
Linkable content is more evergreen that will be alive even after a decade, but shareable content dies soon or after a few days.
It's up to you which type of content do you write.
You should adopt both tactics in SEO for the maximum advantage. From one method, you will get a lot of shares, likes, and tweets and brand awareness, and with the linkable content, you will get more backlinks.