The only way to really learn about investing is to commit a meaningful amount of your own money to the market. Investing "on paper” doesn’t produce the same amount of concentration and attentiveness (not to mention, anxiety) necessary to effectively learn the fundamentals of finance and investor behavior. You have to have skin in the game.
But first, you need to develop a personal, common sense investment plan (and then, of course, you have to actually follow the plan).
The plan should be customized to your particular investment objectives and your own unique tolerance for risk (which really means your tolerance for loss). It should follow a logical investment strategy that is easy for you to understand, implement and monitor and you should use broadly diversified, low cost (and no-load) mutual funds or ETFs. Asset allocation should be an important part of the strategy to produce a balanced portfolio that will better withstand stock market volatility.
There are a number of good books that can help you get started and provide you with a sound strategy and some well-diversified, low-cost fund recommendations to help you construct your portfolio. I highly recommend reading John Bogel's The Little Book of Common Sense Investing or Rick Ferri's All About Index Funds.
One final bit of advice: Once you have your investments in place, leave them alone. Resist the temptation to buy and sell based on what you think the market is going to do. Monitor how you are doing but no more than once a month.
The first lesson we all have to learn is: You can’t beat the market! So don’t try.
Experience is a very effective teacher, but that education seldom comes cheap. We learn our most valuable lessons through expensive mistakes. But if you can stick to the basics and follow sound investment advice, you can learn the fundamentals and develop your investing skills without losing your shirt.