The CDL is basically an MEL that involves items on the aircraft that if missing or deferred could cause a performance penalty. Things like gear doors missing, flap fairings missing, that kind of thing. You will find the performance penalty in the description of the CDL. For instance, if a gear door is missing, it might say reduce climb weight by 3000 pounds or increase cruise fuel burn by 2%. Usually this is advisory as the dispatcher has already taken these numbers into account.

Are you going through school right now?