Open-end funds are what most people talk about when they speak of mutual funds. There is no limit to the number of investors or shares. The value of the shares (Net Asset Value or NAV) is not determined by the number of investors or shares but by the changing value of the stocks, bonds, or whatever makes up the fund. Your decisions to buy an open-end fund would be based on the stocks or other assets that make up the fund.
A closed-end fund, on the other hand, issues a set number of shares when it goes public, just like a regular stock. These can be bought and sold through your brokerage account just like a stock. The problem is that the share value is not determined by the changes in value of the stocks that make it up. It is more subject to the emotions and perceptions of investors, by how many shares are bought and sold at any time. As such, they are more volatile than most open-end funds and more subject to emotional buying and selling.
Open-end funds, because they are not affected by market sentiment, are more stable and more dependable in their movement. Because the number of investors or shares does not affect the NAV, the changes in value are not so volatile and returns are more dependable. The closed-end fund can be a good investment but it requires a lot more knowledge and skill than investing in a simple open-end fund.