There are no installation instructions.
I'll give a more in-depth description of what I did:
Last week, I logged into the backend of Joomla and went to the extensions tab which took me directly to the Install from the Web view (which is where I always go to download an extension). I used the categories in the left panel to find a comment extension (Contacts & Feedback > Article comments). I clicked on CComment Core (after doing a little research of the extension), and on the confirmation window, I clicked Install and after a moment got the green success message box.
I didn't mess with any setting, I just went to my site to see what the new comment feature looked like and I loved it so I tried to test it. When I clicked the "Write Comment" button, it showed the comment platform but also a warning at the bottom of the screen:
Warning: array_intersect(): Argument #2 is not an array in /home/jeniouis/jeniouis.com/community/components/com_comment/helpers/security.php on line 277
Having no idea what to think of that, I first tried to write a comment and post it anyway but as expected, it didn't work. CComment doesn't provide support for their free version of the product, so after a brief moment of searching online for answers, I simply decided to uninstall the extension.
I returned to the backend of Joomla and went to global configuration where there was an uninstall button for the CComment extension. I clicked it and nothing happened. Then I went back to the extensions tab, this time clicking the manage button. When all the extensions on the site popped up, I searched for CComment and uninstalled the four results (CComment-a component, Content - CComment, K2 Plugin - CComment, Search - CComment) and uninstalled each, manually.
I tried to download another comment extension via the extensions tab but I got the error message. And this is where my original post comes in.
Please note: I was able to reinstall the CComment extension and got it to work this time. I suspect the issue was that it comes with a default gravatar and I don't have gravatar set-up for my users.
However, I'm still concerned this error will prevent me from installing extensions in the future. I haven't tried to install anything else since.