Watch the Shaping Fingernails & Picks online guitar lesson by Muriel Anderson from 50 Right-Hand Techniques You Must Know
If you are just trying to get used to playing with fingernails you can use press-on nails or ping pong balls cut to the shape of your nail. A little glue dot (the rubbery kind) augmented with a small piece of surgical tape or bandage at the base of the plastic nail holds on for about a day or until you peel it off. Cut the artificial nails fairly short and sand the same way you would sand your regular nails. Or go to a nail salon and have some tips put on. Explain it's for guitar playing, strong but not too long!