In order to be able to order different meals, these meals have to appear on your menu first. Additionally, you can determine whether a meal should be on the menu all the time or only on the seasonal one.
In OLAT this means that you have to allow all OLAT users (in learning resources) to access your course by making it visible in learning resources. Otherwise, your participants will not be able to see a published course nor will they be able to attend it. Furthermore, you can determine if you want to allow OLAT guests to access your course.