Des as a partitive article

Partitive articles are employed before a name designating an uncountable reality. It is used in the plural form when no singular form exists for the noun in question.

• Cet été, je prendrai des vacances.
• Il mange des rillettes.

For those two words, the singular form either don’t exist (rillettes) or do not have the same meaning (vacances).

Des as an indefinite article

Indefinite articles are determinants used to refer to something or someone undetermined.

Il mange des pâtes.

To avoid confusion, this site suggest:

To avoid confusion between the partitive article "des" and the indefinite article "des", replace this determinant with "un" or "une". If the sentence does not lose its meaning, it is an indefinite article. If the sentence no longer makes sense, but the word "des" can be replaced by "un peu de", it is a partitive article.