To play the game, you must have installed raylib library in your computer with GNU/Linux (i don't know if the game works on another system, i only tested it on Linux). Check the raylib documentation at https://www.raylib.com/ for C.
Once you have raylib set up. Just do
git clone https://github.com/rxxbyy/pong
cd ./pong
then run the simplest possible build command that gives raylib and run the game
gcc -o pong pong.c -lraylib -lGL -lm -lpthread -ldl -lrt -lX11
./pong
NOTE: vertical player's collisions doesn't works too good