a net網 means “net,” and を marks it as the direct object of the verb. Depending on context, it can refer to a fishing net, spider web, or insect net. In 網を張る, it means “set up a net” or “spin a web.”
JA: 父は魚を捕るために網を海に投げ入れた。
EN: My father threw a net into the sea to catch fish.