Stick with SQL databases for now, and use whatever's easiest in whatever environment you're using. That's probably SQLite on your laptop, PostgreSQL if you're deploying to Heroku, and PostgreSQL or MySQL if you're deploying somewhere besides Heroku. And as soon as you deploy anything that has data that you care about, and will have multiple people using it, make sure to not be on SQLite.
More explanation below:
How much research should I be doing on my own?
Very little. If you're a complete newcomer to programming, you're going to have your hands full as it is. Your choice of database is not the first problem you have to solve.
SQL or NoSQL?
You may have heard of these new-fangled databases loosely called "NoSQL". They're cool, but they're a lot newer than SQL databases, which will cause you troubles when you're getting started. This isn't so much an issue of the technical merits of one style vs. another, but if you choose a NoSQL store that you're going to have an uphill climb with setup, installation, library support, documentation, etc.
SQL, on the other hand, is super-popular and might actually be older than you. That means that for every single SQL question you have, you're only a Google search away from an answer. Stick with SQL for now.
Which SQL database should I use?
There are three meaningful open-source SQL databases: SQLite, MySQL, and PostgreSQL. An over-simplified comparison might go like this:
- SQLite, as the name implies, is meant to be a very light implementation of SQL functionality. You can use it, say, if you're making a Mac application and need a good way to store structured data, but you don't want to go to the trouble of setting up a SQL server. This also makes it great for developing on your own machine, but since it's multi-connection functionality is limited, you're not going to be able to run an app on production with it.
- MySQL is a full-scale SQL server, and many large websites use it in production.
- PostgreSQL is also a full-scale SQL server, used by other large websites in production. This is actually my personal favorite, but that distinction doesn't matter when you're just getting started.
Any of these will get you what you need: A place to store your Rails data and a way to start learning SQL bit-by-bit. You should optimize for ease of installation or deployment. So that means:
- SQLite when you're working on your laptop
- PostgreSQL if you're deploying to Heroku, since Heroku favors PostgreSQL over MySQL
- PostgreSQL or MySQL if you're deploying somewhere else. Check their docs and use whatever they tell you to use.
And it's going to be fine, at first, to have the same app using different SQL engines in different environments. At some point you may end up using some really specific, optimized SQL that SQLite can't run, but that's not a newbie problem.