You are referring to the front page of the site. The set of questions there is determined by the selectors (tabs) to the right - active, featured and so on. Hovering over the tab name will show the criteria used by the tab. The default tab is active, which lists questions by most recent activity such as answers and edits.
Perhaps calling this view "top" is a bit misleading. This word makes more sense on StackOverflow, where the default tab works differently. But in a very weak sense, the questions on the front page are "top scoring questions" - namely, the questions scored $<-3$ do not appear there.
As for a link to the top questions page, there is one: it is the word Mathematics set in very large font, in all caps.