An diesen Stamm werden die starken Präteritumendungen -st, -en, -t, -en angehängt.
In front of the cottage was a garden in which two rose-trees stood, one of which bore white and the other red roses.
You spoke to Mr Wolf yesterday.
In the 3rd person singular, both bäckt and backt are possible.
In German, unfortunately, you have to remember different endings - as usual.
Originally the distinction was as in English: The Präteritum was the standard, most neutral form for past actions, and could also express an event in the remote past, contrasting with the Perfekt, which expressed an event that has consequences reaching into the present.
Germans commonly opt for the Perfekt in their speech in order to refer to the past — which will be discussed in my upcoming post.
If the past action was not completed, one would use the imperfect.
Hier siehst du noch einmal die Formen von sein und haben im Präteritum.