Once you have downloaded the Zip file, it should be extracted into your Arduino Libraries folder and the folder renamed to "LEDSync".
This class aims to make using and synchronising multiple Teensy 3.x boards easy. It uses the undocumented pull-up function of a digital input to achieve this. Each board should have their READY_PIN connected to their WAIT_PIN using a 1N4148 signal diode, then all the WAIT_PINS of each board should be commoned. The class also allows you to specify upto 5 ID pins which can be permanently wired to ground to enable unique board numbering, thus allowing for upto 32 boards.