Azure DevOps Server/Team Foundation Server

 

TFS wasn't designed specifically to support a requirements management process.

Epics are like big stories or groups of stories, are written in the language of the customer, and it is kind of a large initiative. it might take several sprints.

Features are the groups of functionalities. a feature can corresponding to one or more stories. a feature can be distributed. shipable unit, almost like a mini-requirement. They're tied to specific delivery dates.

stories are about the values. a story is like to finish in one sprint, are broken down or decomposed from a listed of features. A feature might have several user stories. 

Epics are the primary business value language, can only be connected to features which are basically little bits of functionality into user story.

In the Scrum process in VSTS/TFS a "Requirement" would be represented as a "Product Backlog Item".