The shikai (始解, initial release?) is the first "upgraded" form available to a zanpakutō. To activate it, the shinigami needs to learn the name of their zanpakutō. This is not as simple as simply picking a name, as the living spirit of the zanpakutō chooses its own name. Therefore, the shinigami must be able to communicate with their zanpakutō effectively. Achievement of the shikai is a mark of expert control of a zanpakutō, and it appears to be a requirement for advancement within the shinigami ranks, as most seated officers and presumably all lieutenants are capable of shikai.
After first learning the zanpakutō's name, the shikai can be performed at will simply by speaking a command followed by the zanpakutō's name. The command phrase varies between users and often relates to the zanpakutō's signature ability, or hints at the nature of its spirit. This step may be bypassed by expert shinigami, usually those who are at least approaching discovery of their final release. In rare cases, a zanpakutō, once released, will remain in that state and will not have a sealed state. Such zanpakutō are described as a full-time released form type.
Once the shikai is activated, the zanpakutō will change form to access whatever special abilities it is capable of. They usually remain in the form of a sword, but the type of sword differs radically among various zanpakutō. The special abilities of the zanpakutō, like the zanpakutō itself, have specific names that usually must be announced to fully activate the effect. As Ichigo's zanpakutō, Zangetsu, explains, knowing the name of an attack and not knowing it makes a difference in the amount of power that attack has.
examples of shikai's
Ichigo shikai

hitsugaya shikai

Renji Shikai

mayuri shikai

((will show you bankai next post to show diffrence)
Bankai- The bankai (卍解, final release?) is the second and final form of a zanpakutō. To perform it, a shinigami must be able to materialize their zanpakutō's spirit in the real world and subjugate it, giving the shinigami full reign over the zanpakutō's power. Because such an act usually takes hundreds of years of combat experience to achieve, it is rare amongst shinigami and almost exclusively limited to the thirteen shinigami captains in the Gotei 13. Byakuya Kuchiki claims that among the four noble houses of Soul Society, only one person in several generations will be born with the spiritual power necessary to achieve it.[3] Ichigo Kurosaki and Kisuke Urahara are exceptions to this fact. Using a special device created by Kisuke, which forcibly materializes a zanpakutō spirit (thus bypassing the experience portion of the training), they were able to attain their bankai in three days, instead of the normal hundreds of years.
After a shinigami is able to materialize and subjugate their zanpakutō's spirit, the zanpakutō can assume its final and most powerful form. Unlike the shikai, there is no command phrase to activate bankai, though the user will usually say bankai beforehand. A zanpakutō's bankai is often a manifestation of the spirit itself, usually creating a massive creature or effect to aid the user in battle (Ichigo's bankai is an exception, becoming more compact instead). Certain shinigami also change with their zanpakutō, gaining different clothing to fit with the form. Most zanpakutō will also gain additional special abilities. Like with the shikai, most of these abilities have an associated name. Maintaining the bankai is taxing for the wielder, and it is difficult to maintain it for long periods of time.
ex.
Ichigo Bankai-

hitsugaya bankai-
Renji Bankai-

mayuri bankai-

TypesThere are several types of zanpakutō, classed by the main purpose or effect of their special abilities. These types include:
Melee-Type Zanpakutō. This classification of Zanpakuto is primarily designed for melee combat rather than a magical ability, and is often praised for its resilience and durability that goes well above other classifications.
Kenpachi Zaraki
Ikkaku Madarame
Sajin Komamura
Makoto Kibune
Kidō-Type Zanpakutō are designed around a special ability rather than its close combat potential.
Yumichika Ayasegawa
Momo Hinamori
Sōsuke Aizen
Retsu Unohana
Hanatarō Yamada
Kaname Tōsen
Kisuke Urahara
There are some zanpakutō that have been shown to have a long distance attack capabilities which allow their wielder to stay at a safe distance from their enemies.
Ranged-Combat Zanpakutō
Gin Ichimaru
Byakuya Kuchiki
Shūhei Hisagi
Rangiku Matsumoto
A large amount of the zanpakutō are shown to be classified by elements:
Fire-Type Zanpakutō
Shigekuni Yamamoto-Genryūsai
Shūsuke Amagai
Ice-Type Zanpakutō
Tōshirō Hitsugaya
Rukia Kuchiki
Wind-Type Zanpakutō
Shunsui Kyōraku
Kensei Muguruma
Water-Type Zanpakutō
Kaien Shiba
Electricity-Type Zanpakutō
Jūshirō Ukitake
Light-Type Zanpakutō are designed to control Light for various effects
Maki Ichinose
Poison-Type Zanpakutō are just as their name suggests; secreting poisons to kill the enemy.
Soifon
Mayuri Kurotsuchi
There are some type of Zanpakutō that are hard to determin a type for. For instance Izuru Kira has a Zanpakutō that doubles the weight of what ever it strikes but it must strike it so it make be a Melee Kido type combination, but this is just speculation. Ichigo Kurosaki's Zanpakutō also falls under this speculation because of its kido and melee capabilities.
Izuru Kira
Ichigo Kurosaki
Renji Abarai
There is a "sub-type" of zanpakutō classification known as the constant-release type, this group pertains to zanpakutō whose wielders are unable to revert them back to their default sealed states after initiating the shikai release. Such a phenomenon is mainly due to the vast spiritual power of the sword's wielder, such that they are unable to completely seal their zanpakutō like other Shinigami. Only two Shinigami are known to have a constant-release type: Ichigo Kurosaki and Kenpachi Zaraki, both of whom have tremendous spiritual power, exceeding that of a normal Captain-class Shinigami.
Dual Bladed ZanpakutõsThough not mentioned, it does seem that bankai makes the effect of the shikai special attacks stronger. The power of Ichigo's getsuga tenshō, for example, increases when bankai is used, and Renji's higa zekkō becomes much more effective after bankai is activated.