Requirements are typically the starting point of a project.
Essentially, a requirement is a single document that defines a feature (or some part of a feature) of a project's end product. Therefore, by definition, a requirement formally states the behavior, presentation and user experience that the end product should have when it is released to the consumer.
A requirement specification is a collection of requirements and is sometimes referred to as a product requirements specification. It typically contains all the requirements related to a product.
Requirements are formal and are usually preceded in the process by documents that capture the thoughts and ideas. These thoughts and ideas form the basis for the existence or need of a feature. Such documents are sometimes referred to as user stories or idea documents.
The Requirements feature allows you to create rich text documents (for capturing ideas, stories, motivations and other reference material) and manage them in one place with the formal requirements.
Requirements and the text documents can be organized in a hierarchical manner, like the file/folder system on a computer.
The Requirements feature is accessible through the Requirements tab and users must be given access to this feature to view and use it.