Link sources allows you define, where you want to lead your social community. When posting your items to social networks, they will be linked to the desired online store (channel) – eBay, Amazon, Etsy etc.  Selecting several channels allows you to set the priority what channel is preferred. If the item does not appear on the first channel selected, it will try finding the product on the second one and link the post to the product page on the second channel,  etc. If no channel is selected (All Available) , the random channel will be selected.