Learn Italian: Torino, simbolo dell'industria, produce molte auto. - Turin, the symbol of industry, produces many cars.

This is the mandatory omission of the definite article in an appositive phrase. When a descriptive phrase set off by commas directly defines a proper noun like Torino, Italian drops the article. That is why we say simbolo instead of il simbolo, even though English says the symbol.

Why is the feminine plural adjective molte paired with auto, which ends in -o?

The word auto is an abbreviation of automobile, which is a feminine noun. In Italian, abbreviated nouns are invariable, meaning their endings do not change in the plural. The adjective molte still must agree with the feminine plural reality of the word, resulting in molte auto.

Why is it dell'industria instead of just di industria?

While English says symbol of industry without an article, Italian generally requires definite articles for broad, abstract, or category nouns. Therefore, the preposition di must combine with the definite article l' to form dell'.