A collection in SuperMemo is made of a set of elements. Each element is a page of information visible on the screen at one time. Elements in SuperMemo can be of three types: items, topics or tasks. 

This is the function of these three element types:

• items are simple elements that are used to test your knowledge. They often have a form of a question and an answer. They can also assume other stimulus-response forms. For example, multiple choice test, spelling exercise, picture recognition, etc.
• topics are pages of new information to learn. Topics may assume one of these exemplary forms:
  1. articles (e.g. imported from the Internet) or their fragments (chapters, sections, paragraphs or single sentences). Topics in the form of articles play a central role in incremental reading, i.e. massive parallel reading of articles imported from the Internet
  2. reference material such as URLs of articles to read, rough notes, pictures to process, etc.
  3. presentation pages created by authors of commercially distributed collections. Presentation pages provide an introduction to a given body of knowledge. For example, a general overview of the history of the Ottoman Empire before individual questions are asked in reference to the same subject
• tasks describe jobs to be done. A task may be an article to read, e-mail to respond to, website address to explore, etc. It can also describe jobs that are irrelevant to learning, e.g. a product on your shopping list or a description of a household chore on your to-do list. Tasks are useful in cases where there are more tasks than your can handle. Tasks are therefore used to prioritize your work. They help you start working with the most important tasks and proceed with less important tasks later  

The division into items and topics is central to incremental reading. Let us then first focus on the difference between topics and items. Topics are used to introduce the student to a given subject, while items are used to rehearse the same subject in order to retain it in memory. Typically, you can import an article from the Internet (this will be a topic), extract its most important fragments (which will also be topics) and then convert it to question-and-answer material. Those questions and answers will be items. Items will ensure you do not forget what you have learnt.

Topics and items are presented for review in the learning process in a different way:

• topics are presented in always increasing intervals. Each new interval equals the old interval multiplied by a constant called A-Factor
• items are presented in intervals that depend on grades you score in the process of learning. Those intervals are determined by the SuperMemo Algorithm

If you generate items from topics in the process of incremental reading, items will usually be children of topics in the knowledge tree. Even if you move items away from their parent topics, you can always jump back to the source topic by using the reference hyperlink button on the element toolbar.

Tasks differ from topics only by the fact that they are kept on one of your tasklists. Tasklists are prioritized lists of tasks. Tasklists which are composed of articles to read are called reading lists. Tasks can also enter the learning process and still remain on the tasklist. For more see: Break free from work overload.

The following table summarizes the differences between items, topics and tasks:

The structure of the knowledge tree will usually be determined by the operations you perform in the process of incremental reading. However, if you create a collection for use by others and would like to build a clear structure of presentation pages (topics) and the testing material (items), see: Building the knowledge tree