Period underwear  is a relatively new invention. It’s like regular underwear, except it’s created with a special fabric that absorbs menstrual tissue and traps it within the fabric.
You can usually use one or two pairs throughout your entire period. Just make sure you wash them according to the manufacturer’s directions after each wear.
Different types have different levels of absorbency. If you have a lighter period, you may be able to rely on only these.
If you have a heavier period, you may enjoy using period underwear as a backup to prevent accidental leakage.
There are a ton of different brands out there, but they all work in a similar way.