Pass recipients have to choose to add it to their Passbook wallet. If the Pass does not require the customer to complete any information, they will see an 'Add' button in the top right corner. Once chosen it will be added to Passbook.
If you want your customer to fill in some personal information they will be presented with the appropriate form (automatically generated from the dynamic fields you chose in the Pass Designer). At the bottom of the form they will see an Apple button 'Add to Passbook'. Once they select that, they will be presented with the Pass and the blue 'Add' button in the top right corner. Select that and the Pass disappears from view and automatically gets added to Passbook.