What's the difference b/w certificates of deposit, money-market deposit accounts and money-market mutual fund?

..and is it good for a young college graduate without a student loan debt to investigate in any of these?

Certificates of deposit (CD's) you lock the money up for a specific term (ex 6 mths, 1 yr) and the rate you are earning is guaranteed for that time frame. You can capitalize the interest which means the interest is placed back in the cd or you can have the interest deposited in your bank account or a check cut to you.

Money Market accounts- are a cross between a checking and savings account. It earns interest but they give you checks which you can write out. You are limited to the amount of checks you write per month. It is designed to save. It is the most liquid of the 3 accounts you have mentioned.

A mutual fund is designed for long term savings. Your money is invested with the fund and can lose in value but also has the potential to earn more. It is riskier than the other 2 options.

Any of these options are good to invest in but you need to think about what your objective is and what you feel comfortable with. Do you need access to the money? What are your plans with the money? When are you planning on using it? Etc.

that's a good question

A certificate of deposit is an agreement between the bank and the depositor for a specified period of time at a given rate of interest. A money-market deposit account is similar to a savings account except you're able to do things like write checks against the balance. Typically a money market account earns a higher yield than a typical savings account. A money-market mutual fund is similar except it typically yields a higher rate of return than a MMD accout, sometimes with more restrictions. About whether or not to invest in these: If you want to invest for the long-term no. If you want to save to buy a car, maybe, if you want to set up an emergency fund, yes. If you have, say, $5000 that you want to invest/save for say six months a CD is a good idea. Generally speaking if you're looking to invest long-term you can achieve significantly higher returns in the stock market than in those savings vehicles. Another way to look at it is based on liquidity, or the ability to convert the savings back to spendable cash . . . a CD is the least liquid and a MMD account is the most liquid (of the three). Yet another way is the yield . . . typically CDs will yield the most and MMDs the least (however the yield is greater than a traditional savings account).