"Laufen" actually means "to walk fast", like you are walking in a pace. But it is also the verb you should use when you are walking at a normal speed. You can also say "Ich spaziere.", but it means "I'm wandering./I'm strolling." like you are sightseeing. You can also use "laufen" when you are running in a hurry. And you should use the verb "rennen" for "to run", as in a running race. I hope I'm clear. :)
Laufen is generally to walk at a rapid pace, but can be used for general walking. Since it means at a rapid pace it is sometimes used (at the speaker's discretion) for walking quickly, it is often used to mean a regular type of run. Rennen is always used when referencing trying to go faster than someone you are racing with. Rennen can be used for running in general as well; again it depends on the speaker's discretion as there is where it can overlap with laufen. So how do you know? You really have to judge it in the overall context... a simple Sie läuft would probably mean "she walks"... if the context suggests at a more than regular quick pace such as using "schnell" with it,... then it would almost certainly be run.. you really don't know for certain in a lot of duolingo's sentences.
If you are talking about a touchscreen device as in an android device like me as I am typing this right now, you can download Touchpal keyboard (highly recommend it) or if you are on an Apple device just touch and hold down a letter and a small bubble of accented characters to that will show (same method applies to the android keyboards).