A banishing is short for The Lesser Banishing Ritual of the Pentagram and it is a ritual that clears the working space, energetically…it is actually a precursor to other, more complex rituals. Those who practice ceremonial magick do it daily as a sort of cleansing and precursor to any work that follows. This way you can be sure that your working space is free of parasitic or malelvolent entities. I follow my banishings with an invocation to the Egyptian Sun God Amoun Ra because of my personal affiliation. Any Goetic/Enochian work too should begin with the LBRP. Basically what it does is it strengthens the light body by drawing upon your light source and bringing it down your spine from the Source into the material realms (Malkuth on the Sephiroth) and reinforcing that by calling upon God-names at the 4 compass points which also correspond with the elements. From my experience it has made dream recall, astral projection and dream lucidity much easier to control and has strengthend my inner sight considerably! You can find many tutorials online with a quick Google search.
Good luck! 🙂