A company code is the organizational unit for financial accounting. A plant identifies a location that plans, procures or holds materials. Purchasing organization and purchasing group describe responsibility for purchasing. Those keys can look similar because a company chooses its own numbering. They are still different fields with different jobs.
Harbor Motion Manufacturing uses company code 1000, purchasing organization 1000, purchasing group 001 and plant 1100 in these scenarios. Storage location 0001 identifies the stock location inside the plant. Read the field label before entering a key. A correct material and quantity can still leave an unusable document if you send the item to the wrong plant or assign the wrong company code.