The three main types of fake nails are acrylic nails, gels and silk nails. As WebMD points out, silk nails are typically used for short-term repair or strengthening, while acrylic nails and gels are more often used on a long-term basis.
Acrylic nails are made of a mixture of a polymer powder and a liquid monomer. They can be used to cover the entire nail or just the tip. Acrylic nails harden when exposed to the air. As the nails grow, the gaps between the acrylic nail and the nail bed must be refilled with acrylic; this is typically done every two to three weeks. Acrylic nails can be removed by soaking the hands in nail polish remover.
Gel nails are polymer resins that are brushed on, then harden when exposed to ultraviolet light. They usually last longer than acrylic nails but also need to be filled in every two to three weeks. Gels are also removed by soaking in nail polish remover, which is sometimes applied in the form of nail-sized wraps on each nail.
Silk nails are fabric wraps that are glued on to a broken or weak nail to strengthen it. Even though they are usually called "silk" wraps, the fabric used is sometimes fiberglass, linen or paper. Silk wraps are temporary and come off by themselves within a couple of weeks.