To have long nails, you could have false ones applied by a nail technician or you could apply some yourself. However, these can damage the nails when removed and make them brittle.
To have natural long nails you will need to grow them. The most important factor is to not bite your nails. Drink lots of water, take a multi-vitamin, use cuticle oil regularly, and use base coats on your nails. The Sally Hansen range of nail varnishes are very good at keeping nails strong and healthy. When your nails have varnish on, don't use acetone to remove it as this can dry the nails out.