Basicly your soul needs to be at a specifix level of release and energy for you to get into actual astral, if you are not at this level and try to force it you enter into what is called mindspace, the collective unconcious mind of the human race, which is basicly like astra, but of no significant use, can't cause any real effect in physical with it etc, sad place really for delusional mind that don't work on their souls.
Basicly astral works in a upward revolving spiral, within this spiral one finds all the various realms of teaching, as one moves through them you gain learning and understandings etc. as one moves upwards one gains alot more understandings of soul, self, and everything in between, the idea is to reach the top, at this point one would usually reach buddha level of conciousness as well as ascend from astral onto the etheric planes, now the etheric planes is where one finds heaven, the underworld and hell, to get onto here one either needs to have worked to the right level of energy which is your 7th auric field permanently fully open, or you need to have a higherself connection which actually pulls you in basicly, now on various level of astral and etheric you will various beings, etheric beings in general stay on etheric but can descend to any of the lower levels, within astral you will various deities, guides, teachers etc. when you reach etheric you will find the gods, and various places of extended learning, such as the halls of knowledge in the underworld and the various libraries in hell. But this is what i know from my own personal experience, use it, don't use it, however, if you get somewhere and you are not sure if it is mindspace or real beings and realms push your energy out of your body and onto it as hard as you can, from another being or actual realm you will get a push back and feel a energy signiature while if you push on images they will in general chane or dissapear.