Ydinosa = the root, do NOT cut

Sarveisosa = cut away

Dogs nails should be clipped frequently, so that they don't grow too long. If you can hear a tapping, when the dog walks, they are too long. Too long nails make it difficult for the dog to walk and stretch the dogs limbs into unnatural positions.

Inside the nails, the is a core/root, where there are veins and nerves. Avoid cutting this, it is very painful for the dog. It is easier to cut the nails of dogs, which have light nails, because, by shining a flashlight through it, you can almost make out where the root is. If you accidentally cut too much, the result is always bloody. it will heal on its own, but you can put some disinfectant on it and hold the nail tight in your grip until it stops bleeding. 

The nails must always be cut using special scissors designed to cut them. Remember to buy them strong enough, newfs have strong nails.
The nails must always be cut in a slight angle, when looking from the bottom, along the dogs paws. It is especially important to keep the dew claws short, because they can easily be torn if too long.

  Excellent diagrams about nail clipping