Most OS X applications, contain — in the Edit menu — a sub-menu called Substitutions. In most cases it contains six items:

• Show Substitutions
• Smart Copy/Paste
• Smart Quotes
• Smart Dashes
• Smart Links
• Text Replacements

What do they do if you enable/disable them?

Show Substitutions

This window allows you to enable/disable and replace Smart Dashes, Smart Links, Text Replacement and Smart Quotes either in a specific text selection or in the whole text. 

Typically the options on this window allows you to apply changes to text you’ve already typed. For example if you have already written some text without using Smart Quotes, you can change them all from here.  

Smart Copy/Paste

Many applications, including Mail, TextEdit, Messages, and Stickies, can automatically insert or delete spaces to ensure the correct spacing when you paste or delete words. This feature is called . 

Daringfireball has an eloquent discussion on Smart Copy/Paste that I invite you to read if you want the technical details about this functionality. I personally never enable it because I prefer to have control over text spacing. 

Smart Quotes

It converts quotation marks to typographical quotation marks.

You can control the format of the typographical quotes in Substitutions or directly in System Preferences —> Keyboard —> Text

Smart Dashes

It’s similar to the option described in the previous section, but applied to the two adjacent minus signs ‘–‘ that get changed into a typographical em dash ‘—’.

Smart Links

It enables the conversion of Internet addresses and email addresses in clickable items. 

Typically if you write www.google.com you can decide whether to make it a clickable link or leave it as pure text. The same thing applies to email addresses. 

Text Replacements

This option simply enable or disable the Text Replacement in System Preferences —> Keyboard —> Text (see figure above). For example you could have a shortcut rmbp that gets expanded into Retina MacBook Pro. 

If your keyboard shortcuts don’t work in OS X, this is the first option you need to check. This setting must be enabled on every single application, so be aware of this.