Yea Sox!!!
In simple english. I own a company. I decide that instead of my owning the company exclusively, I'm going to let everyone share the wealth. Usually this happens when a company needs an influx of cash to do something. So, I make the company public and everyone can own a piece of the company and thus a part in some decision making.
In very simple math, let us say that we decide the company is worth $100.00. And we decide to sell 100 shares for $1.00 each. You can now buy shares in the company. So you buy 1 share in the company and at the time you buy it, it is worth $1.00. That is called the initial public offering or IPO. Now that all or most of the shares have been sold, it becomes a matter of supply and demand. If the company starts doing well, people may decide to sell their shares and make a profit. So everyone wants my share that I bought for $1.00. The market says one share, instead of being worth $1, is now worth $2. I have now doubled my money. You might sell your share that you bought at $2.00, for $2.50. That is how you get a return on your investment. The price of a stock goes up according to how the company is doing, any news items, a fly flew through the window at the wrong time, supply and demand, etc.
Some companies also pay dividends to their stock holders. That is when they take some of the profit and divide it evenly to each share. So, as a stockholder, you get cash back.
This is a most basic explanation because I am not at all good at math or an investment genius. I belong to a stock club and own a few stocks, Disney included. Feel free to correct my info.
Whether or not the stocks go up or down a few cents in value each year is of little importance to me. I just need to know that in 20 years, I'll be able to sell my stocks at enough of a profit to retire on.