Present simple (I work / He works. -- Do you work? / Does he work? -- We don't work / She doesn't work) is used for activities we do: always, usually, often, sometimes, seldom, never, etc
Present Continuous (I am working / Are you working? / They aren't working) is used for activities which are happening: now, at the moment, these days, this week/month/year/weekend, tomorrow
Past simple (I played / Did he play? / She didn't play) is used for activities we did in the past. They are finished and completed (yesterday, last Monday/week/month/year, when..., in 2000, etc)
Past Continuous (I was playing / Was he playing? / They weren't playing) is used for activities which were happening when something else happened. (yesterday at 8 o'clock, at that moment, while, as...)
