Shinigami are souls that have supernatural powers. As such, their bodies are composed of Spiritrons (spirit particles) instead of atoms. This means that just like most other types of spirits, they can only be seen by other spiritually aware entities, which excludes most humans. Nevertheless, they are quite capable of influencing their environment. Shinigami are the personification of death. Their job is to send spirits to Soul Society (the afterlife) in order to maintain a balance of souls between it and the material world, and to exorcise evil spirits. They all have katana known as Zanpakutō, though not all of them carry them. Additionally, they can be injured and die like regular humans, though it takes considerably greater injuries for the latter to occur than it would in regular humans. There are a few runaway Shinigami, namely Yoruichi Shihōin and Kisuke Urahara. Ichigo Kurosaki is what is known as a Substitute Shinigami, which is a Shinigami who gained powers by taking another's. At first, he uses Rukia Kuchiki's powers which he lost during a fight with Byakuya Kuchiki]]. In order to defeat him, he had to gain his own Shinigami powers, which he did by a very dangerous process that almost killed him. This process turned him into what is called a "Vizard." These are Shinigami who have gained Hollow abilities, and use them to gain power far exceeding and beyond that of a normal Shinigami or a normal Hollow.
Additionally, unlike humans, they do not have to eat anything to sustain themselves. Shinigami and other spiritual beings only become hungry when they used too much Spiritual Energy within a short amount of time.
The most prominent supernatural power possessed by a Shinigami is their Zanpakutō, a supernatural sword generated from the Shinigami's soul. Shinigami also naturally give off Spiritual Energy, which varies greatly in magnitude with the strength of a Shinigami. A Zanpakutō is a physical manifestation of this force concentrated into a blade.Bleach manga Chapter 105, page 6.
Shinigami operations are based out of Soul Society, where departed human souls reside. Travel between the human world and Soul Society is extremely limited and monitored, but some Shinigami are stationed in the human world to carry out their duties and therefore must often travel between the two. In addition, it is a crime for a Shinigami to remain in the human world longer than a certain time limit as this is viewed as living a second life.
It is also implied that Shinigami receive salaries, like workers in the real world.Colorful Bleach Omake 4.