Within your Knowledge Base you can use Categories to help you organise the articles in your Collections into chapters, or relate them together as covering the same topic.
Within the Collections, you can add categories and sub-categories. For example, you might create a Collection for a product, use categories for different versions of the product, and then organise sub-categories to focus on specific part of the product in your article.
Categorising your Knowledge Base is a really useful exercise as it helps your Clients navigate your documentation and hopefully allows them to help themselves before they need to raise a support request.