1. Do you have a supplier, his goods are in some form: word,exel,csv, the Secretary sends in the mail, or an open api.
Question to the vendor: what is the format it stores its data.
2. Depending on the answer to the question above, you can build the logic of import.
+ to import one at a time, or synchronized in a given period of time.
+ on off store opencart already exists a lot of modules which make the import of goods according to the standard fields(name, price, category, options, and everything else)
Individual fields you need to add the module.