This is one of several user guides on specific topics. The directory for all user guides is here.
Use the “Vulnerable” selector on the left side of the web page to select which pair or pairs, if any, are vulnerable in your deal.
Choose “Rotate” if you want vulnerability to be assigned in the order it appears on the standard duplicate bridge scoresheet. This mainly applies when you are generating multiple deals at once (that is, if the “Number of Deals” selector is greater than 1), though if you use it with single deals you will get “None” vulnerable because that is the setting for Board 1 on the scoresheet.