Its a little box that plugs into an audio jack and then on the other side you can plug an amp chord into it so you can play guitar through your speakers and shit like that...anyone know?

a 1/4" to 1/8" adapter?

no matter what its called plugin your guitar into a stereo = bad idea

DI box?

maybe you need to tell us more of what you want to do ...

No need for all that... If your Starting out and want to record some of your riff's.. Buy a (Tascam US.144 PC) there pretty awesome for a offspring musician or song writer or someone just starting out.. there fairly cheap.. and it would also work for what your trying to do with your stereo..