Two categories of authorisation exist. A general authorisation lets you operate as an importer at all; without it you cannot clear any goods. A product-specific authorisation is needed only for certain categories, such as food, pharmaceuticals, chemicals, telecommunications equipment, firearms, or used vehicles, and is usually issued by the relevant ministry rather than customs itself.
Apply for product-specific permits well before you place a purchase order, since some take weeks, and a shipment that arrives before its permit is approved will sit in storage racking up charges.