The six realms of rebirth are :
1) Hell
2) Ghost
3) Animal
4) Asura
5) Human
6) Deva
I'm too lazy to type it out, so I'll cut and paste from a website

1. Hell
Suffering is most severe, continuous and everlasting. Those beings
must have committed unforgivable and evil deed, with no regret or
repent. The evil karma determines their existence in hell. They
suffer until they are completely retributed or the evil karma
vanishes. However, for those who committed the Five Offences
(deadly sins), they will stay in hell without any specific time to
be liberated.
The five rebellious acts or deadly sins are:
(1) killing one's father
(2) killing one's mother
(3) killing an Arhat
(4) shedding the Buddha's blood
(5) creating disharmony among the Sangha.
The performance of good or bad deeds, symbolise one's ascending to
the heavens or descending to Hell under the law of karma. It is not
the judgement of any Buddhas or gods, nor is it the judgement of
any Supreme God; it is in respect to everyone's wishes and it
manifests accordingly. In the eyes of the good people there is no
Hell, because they do not have karma with it. In the eyes of the
bad people, there is a manifestation of Hell, because Hell is the
manifestation of their minds. Simply, it is one's own conscience
punishing one's own sins.
The sufferings of Hell include unlimited coming alive and dying
within a single day. The hell that has the most suffering is the
Avici Hell. The suffering of Avici Hell is clearly described in the
Ksitigarbha Sutra. The first suffering is uninterrupted time,
meaning there is no rest. The suffering is continuous, there is no
respire for even one minute or one second. The second suffering is
uninterrupted space. In Avici Hell, space is filled with one or
many persons. If there is a lot of space, a person will multiply
himself until he occupies all the space. So this hell can be full
with only one person. The third is uninterrupted suffering. One has
to suffer all the kinds of suffering in the world. There is no hell
which has more suffering than this Avici Hell. Such suffering is
called unlimited suffering. The fourth suffering is uninterrupted
grade, meaning this hell does not differentiate, whether one is a
god in heaven, a human in the human realm, a hungry ghost within
the ghost realm or an animal within the animal realm. If one
"qualified", anyone can enter Avici Hell and receive the same
treatment. The fifth suffering is uninterrupted life. There are
numerous lives and deaths within a day and a night, and, between
one life and one death, one suffers.
2. Ghost
In this realm, most of the ghosts always live in the atmosphere of
anxiety, illusion and fear. Their desires are never satisfied. The
hungry ghosts cannot eat as their throat is as narrow as a pin, but
their stomach is as large as a drum. Apart from hungry ghosts,
there are also Yaksa, Raksa, Spiritual Ghosts, etc.. Spiritual
ghosts are dwelling in the nature, e.g. trees, mountains and seas,
and protecting the creatures, while Yaksa and Raksa are evil,
malignant and violent.
If one wants to avoid descending into the Realm of the Hungry
Ghost, one has to learn to control one's desires. One cannot have
an insatiable desire. In general, the desires of humans are for
money, sex, fame, food and sleep.
If one desires wealth, one should reason that life only lasts for
several decades, and that this body is illusive and will soon
vanish once one dies. One should be satisfied once one has enough
money to spend. One should not enslave one's body and mind to
constantly pursue wealth causing a disturbance in one's body and
mind and making one a slave to acquisition. Such a person, when he
or she dies, will most likely fall into the Realm of the Hungry
Ghost because of insatiable desire. If we constantly contemplate
this, erroneous thoughts in desiring wealth will slowly
disappear.
An insatiable desire for sex is also one of the greatest desires of
humans. If one wants to avoid it, one should cultivate the
meditation on impurity. Impurity means the impurity of the physical
body. Outwardly, the body is beautiful. Inside are bones covered
with offensive smelling meat. The sensual enjoyments of sight,
smell, sound and taste are only temporary. The beautiful body is
fleeting, like dew, a dream, a bubble or lightning. We must not
become attached to such illusive beauty, for such attachment is a
major obstacle in our cultivation. Everything should be viewed
naturally - not because beauty has moved our hearts. In this way,
we will not be greedy towards the temporary enjoyments of sight,
smell, sound, taste, and touch.
Concerning fame, few people in the world remain unattached to it,
especially in the face of the ancient saying, "People strive to
prove their worth, and the Buddha strives to prove His honour." The
problem concerning fame is pronounced. Think about this: throughout
history, how many people have pursued fame and fought for it? And
how many of them can really be remembered? The world is changing
all the time and sentient beings transmigrate and regenerate.
Life on earth is even shorter; very soon it will be all over like
bubbles and the dream flower. Even the physical body does not last
forever, much less fame and honour. If one does not exist, where is
one's foothold for fame? So, whether it is slander or praise, we
should follow our conscience to uphold our integrity and avoid
asking for fame. Then the greed for fame will subside and an
honourable name will be formed from generation to generation.
Indulging in the desire for good food will become serious. It seems
to be a small matter, but the harm it will cause is great. We
cannot have unrestricted desire for good food because, if we have
insatiable appetites and are constantly changing our taste, it will
be very easy to commit killing [of an animal]. Furthermore,
indulging in too much in food increases the cruel side of our
nature and encourages our animalistic sexual desires. This will
become a major obstacle in our cultivation. Therefore, it is better
to treat food lightly and consume only pure food.
Next, we must consider the fondness for sleep. We have to put a
limit here, too. If we are overly desirous of its comfort, it will
encourage laziness and increase drowsiness. The mind will veer off
the righteous path toward evil. Isn't this horrible?
Hungry ghosts are hungry all the time, if they find food and put it
into their mouths, it will change into flames, burning their
mouths. They are starving, yet they cannot eat. So "hunger" is the
major suffering, and that is why this realm is called the Realm of
Hungry Ghosts.
The Realm of Hungry Ghosts is a form of punishment for greed. This
is one of the three lower realms of existence (the other two are
the Animal Realm and Hell).
to be continued :-