The past simple is used to refer to a point in the past at which another eventA general term expressing that somebody or something does something or that something happens. E.g.: An apple fell on Isaac’s head. was in progressAn action is in progress when it is happening. E.g.: When I arrived he was surfing. ("he was surfing"), had been completeA concept, related to the perfect aspect, expressing that an action has finished. E.g.: He’s finished university.d or had been going on for some timeA concept which is related to our perception of reality; that part of existence which is measured in seconds, minutes, hours, days, weeks, etc.. In this way, the past simple serves as a time markerA verb or auxiliary that marks the reference point of a non-finite form. E.g.: The telephone is known to have been invented by Bell. ("is") He denied being in love with the suspect. ("denied") He must have arrived late. ("must") in subordinate time clauseA group of related words containing a subject and a verb.s of complex sentences, where the main clauseA clause that could be a sentence in itself. E.g.: I wouldn’t go there if I were you. ("I wouldn't go there") When I arrived he was surfing. ("he was surfing") is in the past continuousThe aspect expressing duration, formed with be + verb-ing. E.g.: What are you doing?, past perfectThe aspect expressing completion. E.g.: He’s finished university., or past perfect continuous tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses.s.

When I called her, she was studying.
By the time I arrived home, they had already eaten everything in the house.
When I got to her house, she had been waiting for hours.

Diagrams

Past simple for actions over a period of time in the past
Past simple The auxiliary DID for emphasis