Leadrollerz

Hello to all of you Question 1: The one thing I can't find any information on is "blending" under layer properties...what do all the options do...what are they for? I've messed around with a few as I've gone through tutorials. How do you know to use "Color Dodge" on one layer and "additive" on another? Could someone give me a rundown on these? Question 2: Whats the Difference between "Flattening" and "Merge Layer Down" Some of the tutorials I have been trying call for one or the other, BUT... whenever I use "Flatten" my project is ruined...if I "un-do" and select "Merge Layer Down" I can continue on with the tutorial and get ..LOL...similar results Thank you for your time. -Martin :-) A.K.A Leadrollerz