Present Continuons: auxiliary verb: am, is are. Indicators: now, look, listen, at this moment.
Past simple: auxiliary verb: did. Indicators: yesterday, last week, last year, last month, ago, in 1996.
Past continuous: auxiliary verb: was, were. Indicators: while - as, when, all morning.
Present Simple: auxiliary verb: do, does. Indicators: every day, usually, always, often, sometimes, every day, rarely, seldom