Rather than keeping all your questions in one big list, you can create categories to keep them in.
Each category consists of a name and a short description.
Each category can also be "published", which means that the category (and all questions in it) will be available to all courses on this server, so that other courses can use your questions in their quizzes.
Categories can also be created or deleted at will. However, if you try to delete a category containing questions, then you will be asked to specify another category to move them to.
You can also arrange the categories in a hierarchy so that they are easier to manage. The 'Move category to' field lets you move a category to another category.
By clicking on the arrows in the 'Order' field, you can change the order in which the categories are listed.