if you have an adjective (or a similar structure) with the noun, then you need the article because it means that there are two similar things and the adjective helps distinguish them:
- studio L' italiano *del Trecento; mi piace IL maglione *giallo
with the only noun, the article has the meaning of a demonstrative pronoun, it means "that one" and it has rather an "embellishment" purpose, and it is always better to use it with common objects
- studio italiano = studio l'italiano (languages or study subjects)
- qui c'è il sale // qui c'è sale e pepe (with two objects it is no more needed) OK?
Catch these 2 rules and you'll stay fine in this topic. Ciao!