What does "ain't" mean and how is it used in English?

In this video, Alisha answers 3 questions. - First what does "ain't" mean, and how do you use it? My second question: what does the phrase "wide awake" mean? - What is the difference between "SCRAPE" and "SCRATCH"? - Can you explain when we use “out” and “in” or “up” like when someone says “I go up to the door and i open it”. If it were me, I would say “I go to the door and I open it” what is the difference between the two sentences?