Please create unit of measures as per your business requirement.
UOM can be each, box, kg, meter and many more. Once you create UOM on this screen, then these unit of measures will be available in create product and manage product screen to assign it to product records. Whenever you will create any sales or purchase order for that product, Unit of Measure field will auto populate the value from product record.
Please enter the UOM name and click on SUBMIT, new unit of measure will be created successfully.