There's not really an example, because to a human (assuming you speak english) you won't notice any difference between an application using Unicode text or ASCII text. You only see the difference when you view that application in another language.
When you program an application you have the option of using the Unicode character set (or any oher character set). A lot of applications used to use ASCII becauase they were more memory efficient since they only used 7 bits per character. But now, with applications being used in more than one country programmers are starting to have to use Unicode because they use 16 bits per character. Which means you can display more characters.