Most computers have a built-in audio interface in the form of a 3.5mm microphone jack, but the audio quality you get from that generally won't cut it when it comes to recording music. Simply put, an audio interface is a device that connects your computer to your microphone. While using a separate input method means shelling out money for hardware, the benefits of using a dedicated audio interface far outweigh the extra cost. While it's safe to say that picking the right microphone is critical, it won't do you any good in your home studio without a solid audio interface to plug it into.
Recording music digitally at home is easier than ever, but that doesn't mean you can use just any hardware.