NO NO NO don't buy a clipper if U don't know what U R doing. they make a sanding disc Petty paws for dogs nails. if it's a large dog like mine I use the same disc but in my dremmle. Cutting too close to the "quick" or into it could realy hurt your dog /very bloody The "quick" is the blood vessle inside thier nail
Get dog nail clippers or a pedipaws. Cut a small bit of the tip. Wait a day or so then cut a little more. If your dog has white/clear nails you can see the quick to avoid it. If the dog had black nails, just cut a little each day. The pedi paws is nice because the nail doesn't split.
I COMPLETELY agree with RobertTyrrell!!!!! If you do not know what you are doing, and know it WELL, do NOT attempt to just go out and buy some clippers and think it is that easy. You can really hurt the dog, by cutting it to much, and it is not easy to determine where to cut it. If you can't afford a dog groomer or vet to do it, walk the dog on cement/asphalt, and that will help. I have also filed my dogs by hand with a nail file/emery board like we use on our own nails,
Walks on concrete pavement help trim your dog's nails naturally. Otherwise, you can get a clippers made especially for dogs, just make sure you do not cut off too much or the dog could risk bleeding to death!