Think of it as a piece of pie. If there are six slices in the pie and you have 1 then your share of the pie is 1/6. Now scale that up to the stock market where you are buying ownership of a company.
If the company has 50,000,000 shares of stock and you buy 100 then your share of the company would be 100/5,000,000. If you owned enough shares then you would actually be able to play a big role in making the decisions that the company has to make.
I also explained it in a bit more detail on another page, so I?m just going to give you a link to that.
