Based on your other question, I agree with another poster who recommends you review your 401k materials. Usually you have some choice over how it is invested. For instance, they may have 20 different mutual funds available. By default they probably put your money into a very safe fund, possibly a money market fund. But you can change the breakdown and perhaps split your investments evenly between four funds of your choice.
If you log-into your account you may have to poke around to find it. Also, there will be two different things you can do:
- Change where you have invested the money that is already in your account.
- Change where new contributions are invested.
Good luck.