아무 means 'any'. So 아무도 없다 is 'There isn't anyone=There's no one' 아무 말이나 해봐 means 'Tell me anything(something)'
데 means '~place'. In most cases you can change it with 곳. For example, 갈 데가 없다=갈 곳이 없다= I don't have a place to go.
아무 = any, 데 = place, 나 = used in conjunction with 아무 like "아무_나"
아무거나 = anything, 아무때나 = anytime, 아무나 = anyone
I find it helpful to open Google translate and place it beside this website. Both for Korean to english and for english to korean.
Why are 'anywhere' and 'anytime' sometimes translated the same (아무 데나 ) on Duolingo?
I thought so, too, but they're slightly different: "Anywhere" is 아무 데나 and "anytime" is 아무때나.