Where is database information stored?

I was watching this video: "A Quick and Dirty Example" (https://teamtreehouse.com/library/rails-models/introduction-to-activerecord/a-quick-and-dirty-example)

Instructor Hampton Catlin takes you through a quick creation of a blog app using Ruby on Rails. As part of the blog app, we created Posts (objects?) using the rails console. These Posts had titles and bodies, and I assume the that "title" and "body" became columns for information about the posts in a database.

When using Railss (localhost:3000) it clearly accesses the information we made in the rails console, correctly displaying the title and bodies of the posts.

So here's where I'm confused: for the life of me I cannot find where the information about the posts is stored, and how Rails is getting that information. I looked in the project folder in the \db directory, and checked all the files in there, but some of them are ruby files that just tell Ruby how to create a post object. The others are sqlite3 files (development.sqlite3, and test.sqlite3), but they are just full of numbers. I tried migrating those sqlite3 files into MySQL to see if I could find the information that way, but they end up being empty databases that have no tables or information of any sort (other than a name).

I'd really like to be able to read information that's stored in the database for a project, or even have the ability to manually add stuff to a database using MySQL that Rails can add into an app accordingly. Anyone know how this works??