Dreamcatchers are an ancient spiritual tool that originated in Native American culture and serves the purpose of catching and filtering out bad dreams or energies. The design is meant to mimic a spider's web, where dreams and vibrations are caught and only the good flow down through the feather, into the mind of the sleeping person. Any nightmares, ill intentions of others, and bad vibrations are then trapped in the web when placed in the bedroom or where one sleeps.
Dreamcatchers are also frequently placed outside homes or spaces to protect the energies of those within. They will filter themselves to cleanse the caught energies, but you can also sage/smudge your dreamcatcher to refresh it, or hang it outside in the fresh air and sunlight.