Hyde here from Shopify. Interesting question!
First off, I'd like to give you a sense of what fulfillment actually means through this help document.
So fulfillment is the name for packing and shipping of your order. You need to decide how you're going to fulfill those orders. You could fulfill them yourself or you could use a third-party to do so in the form of a fulfillment service. This depends on several factors, including whether or not you have your own inventory or are dropshipping.
Now in terms of manual versus automatic fulfillment we have a guide here. In relation to automatic fulfillment there's great information here:
Without being familiar with the specifics of your store, I hope this information gives you a sufficient enough overview to comfortably and happily run your shipping. If you have any other questions, please don't hesitate to let me know!
All the best, Hyde.