They work like "while" and "during". Both words talk about simultaneous events, but "mientras" is used to relate two sentences ("Hablo mientras como"/"I speak while I eat") and "durante" is used to relate a sentence with an event described by a noun ("Hablo durante el concerto"/"I speak during the concert"). Hope it helps.
Raise your hand if you are sick of wasting time with that damn bird popping up to give you encouragement, and ads you can't use the back button to escape from.
I wanted to post this earlier, but Duolingo locked threads on earlier lessons. Congratulations to those of you who have come this far. Quit. There are dozens of better apps to learn languages in the app store. Duolingo is poorly programmed, has intrusive and obnoxious ads, ignores their users, and commonly uses incorrect translations to try to teach. I've been using this app for 760 days and it has been an almost complete waste of time. I read Spanish on a 4th grade level now. I can't speak it any better than I could on day one. This app is useless, and if you're serious about learning a language, this is NOT where or how to do it.
You've been warned. This isn't worth it.