Volume equals liquidity (ease of turning a stock into cash). High volume is also a indicator of demand. Thus, it is easier to buy/sell a stock that has a large volume of shares traded.

if the company is going to go out of business, and you don't sell it in time, it becomes worthless, otherwise you should be fine - stay away from Penny Stocks (under $5.00/share) and look for stocks with at least 100,000+ daily volume of shares sold and you should be fine

If it is listed on exchange , but the bid price for low volume,illiquid, large spread stocks will be much lower than the mid-price.

Here is my question. How do I know I can sell my stock in the future for sure. I am not talking about making a profit on it, but simply knowing that there is gonna be market for it. Does the volume of stock indicate anything about whether there will be demand for it? Or selling stock at any time is possible. Like I said, I am not talking about selling at a profit or loss, just simply being able to sell back. Thanks.