A value fund is a mutual fund that has a focus on undervalued stocks. They are typically companies that are more mature and don't have impressive growth plans. They are often called out-of-favor stocks. They may be out-of-favor for a variety of reasons. Sometimes companies have a bad quarter. Sometimes they are in an industry that is slowing down for a bit. It may also be as simple as changing investor preferences. Often these things are temporary and that is what the investment is planning on.
Value stocks are usually stocks with a low P/E ratio. (Investopedia has a pretty in-depth definition of P/E ratio.) Value stocks are usually more conservative and often pay dividends. With a value fund, you should get a dividend payout, plus a return on your investment. This type of investment usually has a lower risk than a growth fund.
But how do you invest in one? Almost all mutual fund companies have a value fund as one of their product choices. Anywhere that you have been investing already should be able to give you access to a value fund. If you've never done investing you should be able to purchase a value fund directly through a mutual fund company. You can also open an account with an investment firm, or use an online stock brokerage account. See "How to make a stock investment". The same process applies here. You just want to make sure that you are choosing a good value fund.
Now the real question is... how do you pick a good value fund? Morningstar has a nice fund search feature. Choose domestic stocks and choose value fund as a screener. Remember to look for a fund with a good track record. It is best to search funds for at least a 3 - 5 year record, and preferably a good 10 year record. If you choose one that has had a terrific 1 year return, you have often chosen one that just had a big run up. Like choosing a value fund itself, choose a fund that is fundamentally sound but that maybe had a bad year or so. Same as the stocks it buys, the fund itself can sometimes fall out-of-favor. As long as you feel that the fund is making the right choices and is fundamentally sound, buying it on sale can be a terrific bargain!
A value fund is a great way to invest in the market without risking everything on one or two stocks. Because they are buying a large basket of stocks, you have the diversity without needing to have the large investment money to go with that. You can often start small and make regular purchases to your chosen fund. This is one of the great ways to build your portfolio. Remember not to get panicked about the fluctuations in the market though. Individual stocks and the markets in general will have good and bad days, as well as good and bad streaks. As long as your chosen fund is still making sound choices, stick with it!