The red one is MIC, and it is connected to the microphone (the earphone with microphone has a red cord inserted in this port). The yellow one is LINE IN, which means audio input. You can connect some devices that input sound (that is, sound is transmitted through a data cable), such as the audio cable of a TV card (so that you can receive TV sound).

The coaxial audio output port mainly provides the transmission of digital audio signals. Its connectors are divided into RCA and BNC. Coaxial audio is an audio interface with input and output functions. Different from the previous audio interface, it integrates the microphone interface (input interface) and the earphone or stereo interface (output interface).