"Handelt" is the second person plural form of "handeln". Here, it's used as an imperative for talking to a group of people. You can see the other forms here https://de.wiktionary.org/wiki/handeln_%28Konjugation%29
I translated it as 'Go easy!', which is often used with a complement, for example 'Go easy on the wine!' (don't drink it all at once). Perhaps 'Take it easy!' would be a better translation, meaning 'Proceed with caution.' 'Don't rush things', 'Take your time.' 'No need to rush.',
By the way, let me take this opportunity to say that Duoling is a wonderful product. Thomas
Perfect yes this is exactly what we would say in English alot of the time is to slow down, your going to fast. Perfect, thank you this is how we would say it. Maybe it sounds weird to non-English speakers because down means well going lower. But if someone is jogging to fast and you cant keep up we say "Slow down, for Christ sake."