A regular Poké Ball features a red top, white bottom, and a black ring going around the center horizontally. In the middle of the Poké Ball, there is a small, silver button which can be pushed to release or call back a Pokémon. The Poké Ball is designed to be portable, so when the Poké Ball is palm sized and when the silver button is pushed, it will grow to full size.
Although the exact dimensions of the Poké Ball are not known, it's probably around 4-6 centimeters in diameter, the button on the center of the Poké Ball can also be pushed to shrink so it is small enough to attach to a belt.
To use a Poké Ball to "catch" a wild Pokémon, a Pokémon trainer will simply throw an unoccupied Poké Ball at the wild Pokémon. The wild Pokémon will then be absorbed into the ball, and will attempt to break free unless it likes the trainer. If the Pokémon has not been weakened enough during the time of catching, it may be able to break free of the Poké Ball (only during the first few moments of its catching, while it's still struggling), which is a good reason to use a stronger Poké Ball over the regular Poké Ball, such as a Great Ball, which is 50% stronger than a regular ball. If the Pokémon does manage to break free, the Poké Ball used to attempt to catch it will break and is no longer usable. Poké Balls can not be used to catch already caught Pokémon (Pokémon belonging to other trainers). It is also programmed not to catch humans. If the red beam hits something other than a Pokémon, (i.e. rice cake) it may, or may not capture it.
Once a Pokémon has been successfully caught in a Poké Ball, it will become loyal to its catcher and will usually obey them. For this reason, a Pokémon can not generally be considered "evil" — a Pokémon is only as evil as the trainer who caught it, however Pokémon can also act evil on their own. It is not known what a Pokémon does whilst inside their Poké Ball. The inside of a Poké Ball is "designed to be as comfortable for the Pokémon residing within", although this is not necessarily true. The Pokémon inside may simply be sleeping, or completely unaware of its own existence. Pokémon are, however aware when inside their Poké Ball — by calling their name, the Pokémon will emerge from its Poké Ball almost immediately.
Rarely even, a Pokémon will release itself from the Poké Ball. To release or recall a Pokémon, trainers either say the Pokémon's name ("call it") or push the small button on the Poké Ball. The naming command is usually accompanied with a phrase — such as Go, Eevee or Return, Bulbasaur!. A Poké Ball can only store one Pokémon at a time. For this reason, a trainer may carry as many as six occupied Poké Balls at once — although they may carry up to 999 spare Poké Balls for catching more Pokémon. If more than six Pokémon are caught, the additional ones will be transferred to a PC.
Poké Ball StorageEdit
Due to the Poké Ball's small size, it is hard to imagine how large Pokémon, such as Wailord, or even smaller Pokémon such as Natu manage to fit inside the Poké Ball. Although this has never been made clear officially, when a Pokémon is absorbed into a Poké Ball, their form "shrinks" and turns into energy. It is possible that the Pokémon are simply stored as energy in their Poké Balls, although this, of course, arouses many other questions, such as how they can return to a tangible form.
Even then, when Pokémon are stored inside Poké Balls, they are shown as chips of data when the Pokémon are transferred to Pokémon box, so maybe they are transferred into data.