To be able to label your products with UDI, you need to assign them a unique number which you can do with GTIN.
Depending on the type of classification your product has, you may also need additional information, also known as Production Identifier (PI). Using GS1 standard Application Identifiers (AI), production information such as batch number/LOT number, production date, and serial number can be entered into a data carrier for example in a GS1-128 or GS1 DataMatrix.