Fulfillment API flow

[Fromm60056]

I am new to Shopify. I am writing an app (in my world, it's a simple program). I would just like to know the steps and setup needed to fulfill an order using APIs. 

At this time I have retrieved the order using an API into my ERP. IN Shopify it says unfulfilled. What are my next steps via APIs to get this order fulfilled and a tracking number entered? 

[gsmaverick]

I'd suggest reading through Shopify's Developer Docs on Fulfillment to figure out which type of app best suits your needs. Without knowing more details about your situation it's hard to provide more specific guidance as "fulfillment" can mean many different things.

[Fromm60056]

I am an IBMi shop. We are a manufacturer/distributor of hair care products. One of our lines sells through Shopify. I am able to use the API to retrieve orders. (also get and update items and inventory). So I do have working APIs in both our development and live environments. I just need to know what APIs I need to do and in what order to tell Shopify the order has been shipped (I guess this means fulfilled) and then load the tracking number in SHopify (typically a 1Z number from UPS). Where does a fulfillment # come from? Is it generated by Shopify or in my program (I guess you call it an app)

I have read the developers doc many times and it simply doesn't answer my questions. 

Thanks for your help!!