Diagram.

RS TX/RX
TX/RX function (from computer) in RS-232 protocol. It’s used by Yaesu or Kenwood for those CAT rig control in RS-232 protocol.

TX/RX
TX/RX function (from computer) in TTL protocol. Both CI/V and CAT use this way.

RTS/DTR
Output control. For most ham radio software setting, RTS is used for PTT and DTR is used for CW/FSK.

AF IN/OUT (Computer sound card based)
AF IN is the audio from transceiver. AF OUT is the audio to transceiver .