DI boxes take the high impedance unbalanced output signal from an electric instrument and adjust it for low impedance balanced inputs of mixing boards and other devices. They are usually small devices and some guitar pedals or preamps can also have an integrated DI box as a direct output for mixers.
It's a good idea for gigging or recording guitarists. Even better for bassists and acoustic players. If you gig a lot or do a lot of studio recording, you should have a good DI box. ... That's because guitars and basses (passive models, which is most of them) produce very fragile signals with very little real power output.
The easiest way to connect your electric guitar or bass to your computer is to use one of the small guitar audio interfaces on the market. Just connect the cable from your instrument to the interface and you're ready to rock. ... You plug the guitar into the device and then connect it to the computer USB port.