"During the winter, we used to make soup every evening."
Translation:Pendant l'hiver, nous faisions de la soupe tous les soirs.
The partitive article (de la, de l', du [de le=du]) is used for unspecified amounts of uncountable nouns such as soupe. In English, it can translate to "some", but it's often just omitted.
Nouns almost never appear without articles in French, so, when translating from English, they must be added.
de alone is a preposition that generally means "of" or "from" (but can have other meanings as well). However, as the sentence states:
" ... nous faisions de la soupe ..." the "de la" is the partitive article or "some" but, as stated above, this is generally omitted in English, which leaves:
"... we used to make soup ..."
To read more see: https://www.duolingo.com/skill/fr/Food
le soir simply translates to "the evening"
Whereas tous les soirs translates to "every evening". See 2. here:
My logic exactly. Sitesurf even gives confirmation here: https://www.duolingo.com/comment/195769/Je-marche-le-matin.