The drum set is the instrument central to the rhythm section. It acts as the motor that drives the group. A drum set can contain a multitude of percussion instruments, but in jazz, it usually consists of only a few parts. The lowest drum, or bass drum, is played with a pedal. The hi-hat, also played with a pedal, is a duo of small cymbals that crash together.
A style resource defines the format and look for a UI. A style can be applied to an individual View (from within a layout file) or to an entire Activity or application (from within the manifest file). For more information about creating and applying styles, please read Styles and Themes.
Android OS is owned by Google and powered by the Linux kernel, which can be found on a wide range of devices. Android is an open source operating system which allows developers to access unlocked hardware and develop new programs as they wish. This means unlimited access to any anyone who wants to develop apps for the phone and places very little restriction on its licensing, so users benefit from masses of free content.