2000 audi a4 injector and engine problems?

i have a 2000 audi a4 1.8t, and it gave so many errors with the OBD2 scanner, i.e. injector cyl 1,2,3,4 open circuit, knock sensor signal too large, knock sensor limit reached, etc.. can anyone tell me what these means and what should i do to fix it? thank you!