Enzymes #2

[Melissa M]

Hello,
 
I am still a little unclear about a few things. Okay is this right? An 
enzyme cannot function unless here is a co-factor along with it (why is 
that) There are two different
co-factors metal ions and co-enzyme. There is something that causes a
reduction to occur. What is that process called?? And also how does ATP
and NAD and NADH evolve? I do not understand this. It seems from my
reading that they suddenly evolve, no chemical reactions what so ever?

If you could help me it would be ever so appreciated for I have a test on 
this on Tuesday!!!
 
Melissa