Executing Python in Maya

Command Line: It could be used any time you need to quickly execute a command. The command line will only let you enter one line of code at a time though, which will not do you much good if you want to write a complicated script. To preform more complex operations, you need the Script Editor.

Script Editor: It is an interface for creating short scripts to interact with Maya.Hold right mouse button (RMB) anywhere in the Script Editor window could access the Script Editor's marking menu.

Maya Shelf: Display --> UI Element --> Shelf
              Window --> Setting/Preferences --> Shelf Editor

Tips:
1) Open a new scene: Ctrl+N
2) Press Ctrl+Enter to command script at Script Editor
3) Highlighting a portion of code and then pressing Ctrl+Enter will execute only the highlighted code.
4) Highlighting code before executing it prevents the contents of the Input Panel from emptying out.