The small, flexible cup is made of silicone or latex rubber. Instead of absorbing your flow, like a tampon or pad, it catches and collects it.
Just before your period begins, tightly fold the menstrual cup and insert it like a tampon without an applicator. Used correctly, you shouldn’t feel it. It’s similar to putting a diaphragm or birth control ring in place.
Your cup will spring open (you may need to rotate it first) and rest against the walls of your vagina. It forms a seal to prevent leaks. The blood then simply drips into the cup.
Some types are disposable, but most are reusable. To remove it, you pull the stem sticking out the bottom and pinch the base to release the seal. Then you just empty it, wash it with soap and water, and replace it. At the end of your cycle, you can sterilize your cup in boiling water.
Like any other product for your period, you can buy them online or over the counter at grocery and drugstores.