Tips are made of plastic normally ABS.

Most types of Salon nail contains a well,
Full well are larger and suited for bitten or short nails and should cover up to 1/2 of the nail  no more.
Partial Well are smaller thinner and applied to longer nails.
 
Tips are glued on the end of the natural nail and then acrylic is then applied over the entire nail. Available in many different colours and designs,

Use only nail glue and NOT Super Glue
Super Glue = Methylcynoacrylate adhesives, such as super glue, is a industrial adhesives which are unrefined, attract moisture and break down in water, are carcinogenic, they yellow, and are not intended for use on either the human body or on porous surfaces.

Nail Glue = Ethylcynoacrylate adhesives, such as hospital grade/pharmaceutical grade adhesives used by dentists and nail technicians etc, developed to be used on the human body. They are highly refined, stable in a moist environment, non-carcinogenic and non-yellowing.