Expressions with OVER: "over there", "game over"... - Basic English Grammar

In this video, Alisha answers 5 questions. - Could you please tell me what’s the meaning of “smush”? - What's the difference between 'in time' and 'on time'? - When or How can I use the word "over"? I've seen it like this: "over and over again"... "over there"... "over the vacation"... "game over"... - Could you explain when we should use plural and singular forms of "year", "month"? For example, how should I say "2 year/years later", "2-year-old boy", "I'm traveling for 2 month/months", etc. What is the difference in this forms usage? - Is it "you and me" or "you and i"?