Tk is an interpreted language, that is, a Tk program is not pre-compiled when executed. It is available on all major operating system platforms, including Linux, Mac OS, and Windows.
Most Tk widgets are actually abstract concepts that require specification of parameters to determine the appearance and functionality of a particular widget instantiation. For example, the width, height, and color of a widget typically needs to be specified, or the number of elements in a menu.
You can find all the available widgets and parameters in the Tk documentation.