Lingerie is made of lightweight, stretchy, smooth, sheer or decorative fabrics such as silk, satin, Lycra, charmeuse, chiffon, or (especially and traditionally) lace. These fabrics can be made of natural fibres like silk or cotton or of synthetic fibres like polyester.
A sexy pair of underwear can stand solo or be paired with a matching cami or bra for a low-maintenance (but high-impact) look. A bikini specifically is a classic cut. Its rise is low, but not too low, and it offers coverage in the back while still looking cute and flirty.