This is not a difficult job, but is important preparation for shows and also to keep your cavy's feet comfortable.
Use small dog or cat nail clippers or the flat human nail clippers. Scissors will split the nails if they cut them at all.
In a white cavy if you look at the nail closely you can see a pink area inside it. Do not cut into this pink area.
In a cavy with dark nails you will have to guess so just trim a little at a time.If the cavy squirms just when you press the clippers you probably have them too high up the nail.
When you first begin to clip nails, have a helper hold the pig upright with its bottom supported in their hand. This gives you two hands to work with. With a little practice you will become a wizard at it!