That new Raspberry Pi computer you just got has a row of 2x20 pin headers on the right side - those are the GPIO (general purpose input/output) pins, and for those of us who like to hack electronics, they are where the real fun lies.
By programming the Pi, you can twiddle those pins high or low, send and receive I2C and SPI data, and access the 3V and 5V power rails.
Unlike the 'classic' Raspberry Pi computers, you can't really stick a HAT, bonnet, pHAT or other accessory/add-on on top...what to do? Give up!? NO! Use this cable, which will act as an extender for all 40 pins to give you a stretch of about 20cm. Simply plug the socket side into the Raspberry Pi with the white mark next to the Pin 1 label. Then on the other side, plug the hat down onto the plug side.
Note: Any Raspberry Pi with a 2x20 connector will work wonderfully. For example Raspberry Pi Model A+, B+, 2, 3, 4, Zero... This cable is not compatible with the original 2x13 header Raspberry Pi Model B or Model A.