K09 i absolutely love your Questions, i mean you are asking about magicks on a higher level which is totally awesome!
alledgedly there are infinite dimensions, each overlapping one another sharing the same meta-physical state, but they're on another level to each other, for example, many theories suggest frequency is their border.
how to access these dimensions?
It is utterly impossible to access different dimensions while still in your body, that being said the reason is, you will not be able to pass flesh over the void in which each dimension stands, your physical body must remain in this dimension, if you where to pass flesh over into another dimension, which is impossible, it would likely throw the whole cosmos out of wack.
To enter another dimension, you would have to create a tear in between one dimension and another, which you would need tremendous caution when doing so. entering another dimension is like throwing a live bird at a dartboard, it isn't precise on how to get to a specific dimension that you would want, however getting back is simpler because you would leave some sort of trail leading you back which you could easily follow.
The astral realm is a dimension, overlapping ours.
My theory is that every physical dimension has an astral of that dimension assigned to it, paired if you will. Also in my theory, the astral is exactly the same setting as the dimension, the mug you left in the dimension will be exactly the same place in the astral, the only difference is the astrals atmosphere makes it possible for energy to be seen, as well as auras, and astral bodies, unlike our physical dimension (unless you have some sort of clairvoyent gift enabling you to do so)I find that casting magick in the astral dimension is easier as you can see the energy you make.
can i make a dimension?
The answer to this is "i have no idea" logic would suggest NO, because a dimension contains a different universe slightly, or greatly different to one another. (if my theory is correct the astral is also paired with these) we are not gods, constructing a universe with living things will require, all if not more than we as an entire populus can muster. i mean shesh, "g-d" built the earth in 7 days, how many days did it take to build the universe?
How to access a dimension
you can access a dimension anywhere, the factor that all dimensions overlap gives the possibility of 1 huge door. the only problem is, entering a dimension from a specific point, you will end up in that specific point in the other dimension. say you were to take co-ordinates of where you are, they would be exactly the same in the other dimension.
Why are there infinite dimensions?
well i'll tell you, each dimension is unique, whether it be 1 tiny detail OR a great massive detail from the others. for example. a massive detail is that human beings here look like the way we do, human beings in another dimension could look all green and metalic, or another, use your imagination. a tiny detail could be, for example, In our dimension, the empire estate building is how tall?, well imagine in another dimension it is 1 cm taller, or shorter, or even 2 cm, or 1.5, or even 1.28374586978574 cm taller, there might not even be an empire estate building in one dimension, or several, the possibilities are endless, and with endless factors to pick at, which leads to infinity factors X infinity variations = Infinite Dimensions!
What are Parallel dimensions?
A parallel dimension is a dimension closely related to another dimension, like brother/sister dimensions HOWEVER, they are totally opposite, for example you could be a boy i one dimension and a girl the other, but still have the same name, thoughts etc.
Parallel dimensions are a tricky thing to explain, reason being that, if EVERYTHING was opposite, it would all be chaos, and some arent even possible, say your name was Shaun i.e Me :P, and in another demension which is parallel you need opposites....what is the opposite of shaun?...i suppose you would "mirror" it being like a mirror and all? so it would be nuahs....which isnt that appealing....
This example might get you confused. Okay say you were a boy, and homosexual, meaning, you are a boy and you like boys. the opposite of that is you would be a girl and like girls? yet if we put it under an umbrella and say you are homosexual in one dimension, in its parallel you are suppose to be straight? but technically you are a lesbien. Which is why it is tricky :P
I hope this helps you. Bear in mind it is 6:23am here and it might not be worded properly.