Well I'm thoroughly dissapointed that there are no achieved theosophists on the org (not really, its not a very common object of study)
Okay, I will now attempt to explain those things as best I can

(which will probably turn out mediocre at best :\)
In light of recent religious debate I'll just say that to understand this you'll have to take a step outside yourself for a minute and open your mind. I'm going to throw you a line of 'facts' according to this study, take them as you wish. First I'll give a quick background and then go into the symbols themselves.
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The eternal power, the infinite oneness, the origin of everything, "God", dosen't exist in the traditional sense. This "God", being infinite, contains no finitity in itself. It has no human traits. There is no such thing as 'an angry god' or a god that feels emotion at all, for these are traits belonging to us, and we are finite creatures. This 'god' simply is the infinite collective of all consciousness and spirit. The universe as we know it today consists of 7 different but coinciding and coexisting planes of being. The lowest plane being the physical, the material world of cold hard experience on the base-level of consicousness. Here physical matter makes up the universe unlike the higher planes which consist of a sort of energy matter or spirit matter. The second lowest plane is the Astral. A step up from the physical, it contains no material matter but finer spirit matter. It is a more abstract world than the physical, but also a world with less limits. Like it was described in ep 26 of Eva, the trade off between abstraction and freedom is directly proportional.
How did these 7 planes come into being like they are now? Well, this is where cosmogenesis comes in and the nature of the universe at large. The 5 symbols basically represent the progression of the universe and its eternal cycle of development.
The first symbol: the plain disc.
This represents the state of the universe in it's great sleep. The universe, it seems, is set to an eternal cycle of activity and rest, day and night, movement and slumber. This is the period of rest, the night, the slumber. It is this point where all is one and infinite. Everything rests in infinite oneness. Nirvana. Scientifically, this would be the period (if it could be called that, since there is no concept of 'time') before the big bang.
There is no distinction between anything, just a plain circle, its plane filled with nothing, completely blank.
The second symbol: the single point inside the disc.
Eventually dawn falls on the universal mind and collective consciousness forms the desire to extend and become defined and finite again. This shows the very beginning of the re-formation of things out of nothing, as the point shows a break, a separation from the circle. Still genderless, it is the first break from infinity into finitude.
The third symbol: Diameter drawn through the circle:
As separation and change progress, the singular is split into the different planes and sub planes. The diameter separating the circuference shows the beginning of duality in the unfolding universe.
The fourth symbol: Horizontal diameter crosses vertical:
This represents the formation of man. Not yet a fully material being, but existing as an abstract thought form of primordial earth.
The fifth symbol: Cross without circumference:
When the circumference dissapears from the cross it means the completion of man's fall into matter. At this point all the planes and universes are laid out and nature has become fully dual and distinct, compared to the abstract whole that it was in step 1. This fifth cycle is where we are right now.
6:?
7:?
apparently, our future and the events of the 6th and 7th cycles are known and out there, but I havent been able to find this stuff out, its a bit less common knowledge and a LOT more protected than the past cycles. Intriguing, and I will find out someday. However, I can tell you what happens after the 7th cycle. Return to origin. Back to square one. The universe folds upward and inward and eventually all is again returned to the sleep of infinite oneness. Again, the scientific and physical world relation to this would be the big crunch.
Eventually, like truest chaos said, dawn comes again and starts the whole shebang over. And it's happened like that, forever. The occasional shadow of the infinite onto the finite. The day and night of the all.
Okay, you can return to regular viewing now. :\