The basic purpose of a sound card is to deliver the computer's digital audio output from its built-in speakers. It uses a digital to analog converter to convert electronic signals into audio signals that are distributed through the speakers.
Sound card and music instruments
Most personal computers now have a built-in sound card that provides satisfying audio quality.
However, musicians who need professional sound quality may need a separate sound card.
When it comes to musical instruments, a sound card acts as an audio interface that converts audio signals from the music instruments and converts it into digital signals, which the computer can decipher.
Connecting musical instruments to sound cards
USB ports typically provide connections for various components. For instance, they are used to connect keyboards, mice, printers etc. They also enable connections for storage devices, external hard disk drives and different specialized devices.
If you want to connect your music instruments to the computer sound card, you need a MIDI port. MIDI (Musical Instrument Digital Interface) is a standard that digitally represents and transmits sound. MIDIs are intended to record audio and also record musical instructions.
MIDI software can be helpful to musicians to change aspects of the music. When you record your music through a MIDI port, the software will account for the tempo, vibration, pitch volume etc. The MIDI sound is then produced through a computer
Alternatively, and much easier is to use an audio interface to connect to your guitar to your PC.