Is selecting the online sales channel necessary for selling products on Shopify?

I am new to Shopify, I have added products and made them active, do I have to make sure the online sales channel is selected in order to sell products from my store? I will have thousands of products should I keep selling when out of stock since not all products are at my physical store. Must products I just ship direct from the mfg. to the customer.

Hey thanks for the input, yes I will continue to sell when out of stock, because inventory updates every week. In my business large items of furniture is ok to have updated weekly. My stock mostly comes direct from factories.