Demonstrative pronouns (this one, that one, the one[s], these, those) refer to a previously-mentioned noun in a sentence. Italian demonstrative pronouns are more complicated than their English counterparts, because there are two different sets and because they must agree in gender and number with the noun they replace.
The partitive article (del, dello, della, dei, degli, delle) refers to an unspecified quantity of food, liquid, or some other uncountable noun. English has no equivalent article – the partitive is usually translated by the adjectives “some” or “any,” or may be left out entirely.
Like English nouns, most Italian nouns have singular and plural forms. In addition, Italian nouns referring to people and animals often have different masculine and feminine forms, which means that these nouns can have up to four forms.