If you use your computer via a purely graphical interface, you will typically double‐click the Wolfram System icon to start the Wolfram System. If you use your computer via a textually based operating system, you will typically type the command mathematica to start the Wolfram System.
|use an icon or the Start menu||graphical ways to start the Wolfram System|
|mathematica||the shell command to start Mathematica|
|text ending with Shift+Enter||input for the Wolfram Language (Shift+Return on some keyboards)|
|choose the Exit menu item||exiting the Wolfram System (Quit on some systems)|
When the Wolfram System is first started, it displays an empty notebook with a blinking cursor. You can start typing right away. The Wolfram Language by default will interpret your text as input. You enter Wolfram Language input into the notebook, then type Shift+Enter to make the Wolfram Language process your input. (To type Shift+Enter, hold down the Null key, then press Enter.) You can use the standard editing features of your graphical interface to prepare your input, which may go on for several lines. Shift+Enter tells the Wolfram System that you have finished your input. If your keyboard has a numeric keypad, you can use its Null key instead of Shift+Enter.
You should realize that notebooks are part of the "front end" to the Wolfram System. The Wolfram Language kernel which actually performs computations may be run either on the same computer as the front end, or on another computer connected via a network. Sometimes, the kernel is not even started until you actually do a calculation with the Wolfram Language.
The built-in Wolfram Language Documentation Center (Help ▶ Documentation Center), where you might be reading this documentation, is itself an example of a Wolfram System notebook. You can evaluate and modify examples in place, or type your own examples.
To exit the Wolfram System, you typically choose the Exit menu item in the notebook interface.