When you use PP3 you have to tell the program e.g. which star you want to delete from the map or which nebula shall get a different label. For this, every sky object must have a distinct name in PP3.
By and large there are two kinds of objects in the sky: stars and nebulae. Astronomers have created many catalogues of them. There are two star catalogues and three nebulae catalogues supported in PP3.