Do you want Greek characters or do you want equations and expressions that include Greek characters? If you want just the occasional Greek character, then you will find them in the Symbol font. You will find many of them in each Latin (used by English) font. These can be accessed from the Character Palette found in most applications at the Edit/Special Characters... menu selection. If you want an equation/expression editor, then you should know that Apple endorses MathType Lite. Download the MathType equation editor from DesignScience's website. MathType is the big brother of Equation Editor, the captive equation/expression editor that DesignScience provides for Microsoft and other developers for inclusion in their document preparation software. In 30 days, the MathType demo converts to MathType Lite if you don't pay for it.Scientific formulas use a lot of symbols, including greek letters to represent units of measurement. How can I get a greek letter into an english Pages document?
The way to get a Greek letter on the Mac is:
Go to Systems Preferences> Languages & Regions > Keyboard Preferences
click on the + sign bottom left and select Greek from the drop down menu.
Also select Show input menu in menu bar
Quit Systems Preferences.
Now in the menu bar, by the date will be a flag indicating the language used.
Select Greek and Show Keyboard Viewer.
This will show the keyboard with Greek letters.
Select the letter one needs.
Return to the flag and select the flag of the country of your usual language.
The above solutions mostly are not available in the newer Pages 5.2.
The Edit>Special Characters no longer gives useful characters, but mostly amusing but non-essential images.
The Character Palette has Latin but not Greek letters.