The Invocation of the Forces of the Square is the primary rite, and is used primarily to enliven the Talisman or Gamahe. Both the Talisman and the Gamahe serve as a Material Basis-a physical form created for the spiritual force invoked to inhabit. The Talisman is an Image created to represent a force; a Gamahe is different in that it is abstract, consisting of sigils, shapes, numbers, etc. carved into wax or written upon blessed parchment. This ritual is at the heart of our Thaumaturgy. By carefully joining precise ritual timing, incantation, and intense and focused visualization paired with intent, we can focus the Planetary forces into a Material Basis, and use those focuses to work our will.
The Evocation of the Spirit is, performance wise, very similar to the Invocation of the Forces. Near the end of the ritual incantations, instead of Invoking the Spirit, he is evoked into appearance on the Astral plane, where the magician may go and meet him in the Mental body, or scry him within a crystal or mirror. The Evocation to the physical plane is possible as well .although generally unnecessary. The point of the Evocation is to communicate your will to the spirit directly, and this communication is easily done on the Astral. To evoke a Spirit to the physical merely to satisfy one's curiosity is a bit rude, in my opinion, and may result in negative results. There may be times when Evocation to the Physical plane is necessary-consult with the Spirit to determine whether they are willing to come to the Physical, and if that is necessary for the work you wish them to accomplish.