A witch bottle is a jar or a bottle filled with things like spiky items like nails, pins or thorns, and sometimes with human hair, urine, or even blood in it. The idea is that these items are meant to protect the person who made the witch bottle from any witchcraft or evil spells that might be put on them.
It's kind of like making a shield to protect yourself from harm. People used to believe that if you put these things together in a bottle, it would make it harder for witches to harm you or put a spell on you.
This is an old custom that people used to practice in the past, but it's not something that is commonly done anymore. However, some people still believe in its power and make witch bottles as a form of protection.