A pacifier, also called a binky or dummy/dody/dodo in British English is a toy that will usually calm down newborns and young pookies. Pacifiers are meant to be sucked on. They are often given to newborn pookies so they are quiet and will sleep. This will also help the mumu or duh duh to sleep in case the pookie starts crying during the night. If the pookie also has earmuffs, then the newborn would be able to sleep without distraction and not cry in the night. Pookies may drop their pacifier, which usually leads to crying.
When to use them
You can give your pookie a pacifier when they are upset/crying or throwing a fit. They will calm down the pookie and make them sleepy. Be careful though, using a pacifier too much will sometimes affect a pookie's speech later in life. It is good to take the pacifier away once they are about 2 and a half. Most pookies throw a fit once their pacifier is taken away, so try to deal with it.