The shareasale datafeed file format
You'll have downloaded a datafeed by now. If you look in the file you see line after line of text, with values separated by '|' characters. While this is a "comma-separated-values" (CSV) file, in this case they use '|' characters instead of comma's.
Shareasale documents the file format in their help center: Help Center » Knowledgebase » Affiliate Topics » Product Links » Datafeeds
A comma-separated-values file is a series of lines, each line being one "record" in the file. Each lines has fields in a specified order, the fields are what is separated by the '|' characters. The first field is the Product ID, the second field is the Product Name, the third field is the Merchant ID, the fourth field is the Merchant Name, and so forth. The exact ordering of values in the file are are documented in the Shareasale help center.