How to type Chinese on Mac OSX - Lion, Mountain Lion, Mavericks
Go to System Preferences...
Choose Input Sources, then click +
Select Chinese (Simplified) - Pinyin - Simplified then click Add
Make sure Show Input menu in menu bar is checked.
Use the language icon in menubar to switch modes.
Typing in Chinese using Pinyin
Type in Pinyin, and select the character.
It is a good idea to create a keyboard shortcut to switch between input modes. Control + Space is a popular choice.
Go to System Preferences...KeyboardShortcutsInput Sources
Check Select the previous input source and set the shortcut to ^Space
What native Chinese people actually do:
Most people who live in mainland China install a 3rd-party input method. Sogou Pinyin Input is very popular.
The Sogou input method has advantages:
It is partially cloud based, and will add new words as they become common in Chinese.
It learns from what you type. For instance, if your home address uses a rare Chinese character, it will learn this and make it a top suggestion, rather than requiring you to frequently scroll through lists of characters.