For the purposes of this post, a "Portal" is defined as a gateway through which communications with non-corporeal entities can be established.
All magickal acts consist of working with non-corporeal entities, whether they are gods, demons, angels, egregores, eidolons, or servitors. I prefer the term "Spirits" to non-corporeal entities. It's more personal. The entities we work with are generally self aware to some degree, and thinking of them as cold constructs with no will of their own can lead to all kinds of problems later in your experiences with the spirit realm.
To get the spirits' attention, we have to open a portal between our normal reality and the realms they exist in. There are many ways of accomplishing this, but all seem to include intoning specific god-names. The Druids are recorded as calling out their curses on the Romans, and throughout the Eastern mystical paths mantras are intoned to bring about access to higher states of consciousness. I don't know what the mechanism is, but vibrating aural tones creates changes in the environment.
Once the environment has been changed through the intonation of the "words of power," it is necessary to get the specific Spirit's attention. This is done by having an image of the spirit on hand. There are catalogues of the symbols and seals of the spirits we have made contact with as magicians over the centuries contained in grimoires and described in sacred texts.
Having the symbol or talisman of the spirit we wish to contact, we call the spirit by its name(s) and ask/order it to appear by the "power" of various associated god names. I believe that vibrating these god-names further tunes the portal that is opened at the beginning of the rite to the specific energies that are compatible with the desired spirit, and incompatible with any other spirit. When the environment is sufficiently tuned, the spirit can appear, and communications can commence.
In the Lemmegetton, there are records of the spirits appearing at first in forms that are horrible to look at, and acompanied by noxious fumes and gases. To eliminate this, you are instructed to hold a ring in front of your face inscribed with specific names of God, and to order the spirit to appear in a particular form by the power of specific god names. I think that what might be happening is that the connection of a partially tuned portal must be more finely tuned once the spirit begins to appear. After this has been accomplished, the spirit is comfortable and can communicate quite well.
In 1918, Aleister Crowley performed the Amalantrah working in New York. During this ritual, he opened a portal to other dimensions, and called various entities through it to communicate with him. One of these entities was LAM, which resmebles what we now call "Greys," those pesky aliens that are seen during what science calls sleep paralysis and occultists know as night hags. After he finished the Amalantrah working, he carefully closed up the portal he opened.
Years later, in 1947, Jack Parsons and L. Ron Hubbard performed the Babalon rite. They were attempting to create a Moonchild, a human body that contained the spirit of Babalon from Revelations. It is postulated among many occultists that the rift they opened to draw down the star spirit was never properly closed, and this portal remains open to this day. 1947 marks the beginning of the UFO sightings that swept the world. Another connection between the interdimensional astronauts and the occult.
As this example demonstrates, there is an important need to close a portal after you've communicated with a specific entity. This is done rather simply by performing an LBRP. Thank the GD for that contribution.