To give a practical example. Lets say you have a certain webpage to fetch/render some information based on the user (thats logged on) and language of the browser. The logic of fetching the information is independent from the user and the language. Your page will receive a user and a language ... for the logic it doesnt matter if it is me or you or english or spanish.
Some pseudo code:
class FooPage
{
void handleRequest(RequestContext context)
{
User user = context.getUser();
Locale locale = context.getLocale();
… do some logic based on the context
}
}
Its not that difficult, but it takes some time to understand the concept