Where can I be reborn to?
The Buddha taught that there are six realms of existence (Samsara - this world of pavalent suffering) that we are continually reborn into. These six realms correspond to the six mindstates that we fall into again and again due to Craving, Aversion and Ignorance.
These six world are physically existent in our world and other dimensions - some seen and others unseen. They are worlds manifested through the force of Karma of sentient beings. The six realms are also psychological worlds (mindstates) that we repeatedly get in and out of in this life (or even in one single day). None of these six realms are permanent - not even Heaven or Hell.
The moment the Karma of one's existence in that world exhausts, one is reborn accordingly to residual karmic forces. The first three worlds are called the lower realms - where great suffering is prevalent.
The other tree worlds are called the higher realms - where there is generally more happiness, though suffering still exist. None of these worlds is a safe refuge (not even the realm of gods). All Buddhas have broken free of rebirth in the sinx realms, though they can choose to manifest into them out of Compassion to teach sentient beings the Dharma.
The six realms of existence are: