A function is where something actually does something. Sorry, that's a hard sentence to make sense! Hopefully examples might help: A gas cooker might have a flame-out function, or an auto ignition function. A fitness tracker watch might have a heart rate function or a GPS tracker function. A feature is something that makes something more attractive or different somehow. Wooden inlay on a car dash, and an easy clean surface might be features. So - functions could be features, but not all features are functions.

Here is one example of use. I love my new CubieWink alarm clock. It has the same functions as any other alarm clock--you can set the time, you can set the time of the alarm, and you can turn the alarm on or off. In fact, it has fewer functions than my old one, because my old one was a clock radio and this is just a clock. But the CubieWink has some unique features that few other alarm clocks have. One feature is that it displays AM and PM in letters, rather than just a little on-or-off light. Another feature is that it shows the alarm setting all the time. There is a little picture of bell underneath the main time display. If the alarm is off, it shows the word OFF next to the bell. If the alarm is on, it shows the alarm time in small numbers next to the bell, and, again, with the letters AM or PM.