Congrats on the win!
Here's a thread I made awhile back, it explains all the different blade lengths.
http://www.yorkietalk.com/forums/yor...room-home.html
#10 is very safe to use, that's perfect for sanitary trims which includes their privates, ear tipping (only the flat flaps) & trimming under paw hairs. You can use #40 for under paw hairs but I would not use it for their privates...can cause clipper burn, that's when the hair is clipped too short & can cause an irritation on their skin, making the dog lick it & cause more issues. Using a #40 can cause more nicks than using a #10. Vets use #40 blade to so surgical shaves.
The #30 or 40 can be used under a comb. You can use #10, this is the blade that comes w/the clipper. For combs, start w/the biggest & work your way down, that way you'll achieve the length you want. Same w/ blades. For blades, remember: the higher the #, the shorter the cut.
Here's a video where it shows how to hold the clipper @ 6:25:
He's using a#10 blade to shave the body, I would personally use a #7F or #6F for soft cottony hair & #6F or #5F for fine silky hair. I don't like that 'shaved' look. You can always start w/a longer blade & go shorter if you wish.