This is a type of "fundoshi-style T-back shorts (for men)." ◆ How to wear it: 1. The triangular cloth part goes in the front (covers the private parts). 2. Wrap the long elastic string around your waist and tie it. 3. Pass the elastic string under the crotch through the gap between your buttocks and connect it to the waist string to secure it. In other words, it's a "T-back (fundoshi/swimsuit-style)" with a small piece of cloth covering the front and strings in the back. When worn, it's designed to fit the body like swimwear or underwear. Unlike regular briefs or trunks, it exposes a lot of skin, so it's often used for cosplay and events. The size is unknown, but it's probably free size. Instant purchase is okay.