Features are the menu; non-functional requirements are how fast and how hot it arrives.

A functional requirement names something the system does: upload, follow, comment. A non-functional requirement describes a quality of that behaviour: how quickly it responds, how often it is up, how much load it takes, how fresh the data is. A useful test is whether you can measure it with a number or a percentage rather than ticking it off as present or absent.

Read it once, then a question tests whether the trick stuck.