Well like anything it depends what your personal goals are. Investing? Trading? Starting a business?
/r/finance, /r/personalfinance, /r/investing are decent. I'd stay away from the super-generic places like /r/economy because there's more usually more fluff in there than you'd ever need. If you wanna look at trading visit /r/wallstreetbets. Anyway most subreddits have useful links in their sidebars that will take you to some of the best resources to learn about this stuff.