First, have in your mind what the function of the chunk of code is. If it's not important to the system, skip it, don't read it. If it is important to the syste

First, have in your mind what the function of the chunk of code is. If it's not important to the system, skip it, don't read it. If it is important to the system, take a guess how you think it should work, how you would probably implement it if you were the original develop. Then begin reading it.