In order to exchange data between two devices (eg. autopilot and GPS), the NMEA standard was introduced.
One device sends (eg. the position from a GPS), and at least one device receives (eg. an autopilot). The data is transmitted via a 2-wire cable (2.0 x 0.25 mm²). When connected to the PC, only the NMEA data cable must be connected to a SUB-D connector for the serial port of your PC.