When you arrive at the checkpoint, you must declare all dutiable goods, controlled goods or prohibited goods at the Red Channel. You must show these goods and your import licence, or authorisation where applicable, to an ICA officer for examination, and seek Customs clearance. Making a false or incorrect declaration is an offence.
If you do not have the import licence or authorisation, an ICA officer will retain the item and refer it to the relevant authority for approval. You will be given a warehouse deposit receipt to claim your item after the relevant authority has issued approval to bring it into Singapore.
If in doubt, please proceed to the Red Channel to make enquiries.