To add a promotion extension, click on “More asset types” and select “+Promotions”.
Fill out the required fields.
You don’t have to pick an occasion for the deal but there are a couple of different occasions that you can add if there is that sort of location. For example you have a deal on Father's Day and you add a father's day extension. The great benefit with that is that Google is going to be favoring these kinds of ads, putting them higher up and more likely to show the extension if it is Father's Day. Thus, if you select the appropriate occasion when it actually is on occasion it will increase the chance of triggering your ads and extensions.
URL Options — use this when you want to set up the tracking template
Advanced Options — use this option to actually decide when you want your extension to be running.