It is said in Castanedas books [cc7, i think] that the Universe consists of bands, or filaments, of energy (lacking better terminology) of different kinds. These bands emanates from a source called 'the Eagle'. The bands are organized into bundles. Humans are made up of a small number of these bands, and these human bands exists within us and also, at the same time, on the outside of our luminous body.

The bands inside our luminous body decides what we are and what we can be. One may say that this is our total potential.

According to Castaneda, the assemblage point is a point of the size of an tennis ball located on our back, and at the height of the shoulder blades. The position of this ball determines our perception. Movement of the AP thus changes our perception. Movement of the AP is classified into 'Movements' and 'shifts', where the latter is small movements. 

On the luminous cocoon there is a band which is called the human band, and this is where humans have their assemblage point located.

One interesting thing with the assemblage point is that its location is 'contagious', one persons AP may influence another persons AP. Several factors decide who's AP moves others AP's. Energy is one such factor, but time and situation is another. For instance, during 'favourable conditions' one hysteric person can create mass panic.

The AP is influenced by locations, other people, dreams, situations, worries, thoughts, the will, ones personal energy, food, drugs, practices like tensegrity, tai chi or yoga, practices like meditation or recapitulation and by your breathing etc etc. Colours also influence the AP slightly, music as well.