The Präteritum can only express the past.


Examples time
Er arbeitete als Student bei der Post. past
Sie besuchte jeden Tag ihre kranke Oma.
Lisa verabschiedete sich von ihren Freunden.


Präteritum vs present perfect


The Präteritum is often used in written texts and, mostly, in narration. In the spoken language, the Präteritum of the auxiliary verbs sein and haben and of the modal verbs is mainly used. Otherwise, in the spoken language, the present perfect tense is used to refer to past events. 


The Präteritum can be interchangeably used with the present perfect without any difference in meaning, unless it describes an event that refers to the present time. In this case, only the present perfect can express an event that has been concluded in the past but its results are still present at the moment of speaking.


Examples tense reference to the present
Die Straßen sind nass. Es hat nämlich geregnet. right yes
Die Straßen sind nass. Es regnete nämlich. false no