People, especially musicians, who want more quality than their computer's inbuilt audio hardware, they use a good quality USB audio interface.

A good USB audio interface have a Hi-Z input, zero-latency hardware direct monitoring, Built-in MIDI I/O, iOS compatibility, DAW software and solid build.

The best two-channel USB audio interface: Tascam US-2x2 (good quality sound, solid build, built-in MIDI I/O and iOS device support, portable)

The second best USB audio interface: PreSonus AudioBox iTwo (Has Sonus Studio One Artist recording software)

The USB audio interface with more I/O options: Focusrite Scarlett 6i6 (MIDI I/O and iOS device support)

The best affordable USB audio interface: Blue Microphones Icicle (converts any regular microphone into a USB microphone)