Learn Italian: Sono andato nella nuova salumeria per comprare del cibo. - I went into the new delicatessen to buy some food.

Del is the partitive article (formed by combining the preposition di with the definite article il) and translates to 'some' or an unspecified amount. In Italian, you generally use the partitive article to express an indefinite quantity of an uncountable noun like cibo (food), whereas in English you might just drop the article and say 'to buy food'.

Could I use qualche or un po' di instead of del to mean 'some food'?

You cannot use qualche because it must always be followed by a singular countable noun, and cibo acts as an uncountable mass noun here. However, you can perfectly use un po' di cibo (a little bit of food). It means essentially the same thing as del cibo, though un po' di can slightly emphasize a smaller amount.

Why use per comprare instead of a comprare after a verb of motion like andare?

While it is very common to use a + infinitive after verbs of motion (like sono andato a comprare), using per + infinitive is also correct and strongly emphasizes the exact purpose or goal ('in order to buy'). Both are acceptable here, but per sharply highlights your specific reason for entering the deli.

Why does the adjective nuova come before the noun ?