So the translation for (You’ve been learning about a month) was Usted lleva aprendiendo desde hace aproximadamente un mes. Couldn’t you just omit desde hace here? I believe hace can mean “ago” but I still really don’t understand what desde is for?
Tagging @Deborah-SSi and @gabycortinas for more detailed stuff - but basically that’s performing the function that you’d get with ‘since’ or ‘for’ in English (and I think that prompt sentence would have been ‘You’ve been learning for about a month’)… but yes, you could leave it out and there’d be no problem in understanding… 
Yes, my understanding is that the ‘desde’ is because it’s ‘since’ that time you’re been learning (and you still are).
Just having ‘hace’ on it’s own is ‘ago’ like you said @tim-rippelmeyer, so it’s thinking of that particular time in the past - something you did ‘a month ago’ but not still doing.
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Ok. That makes a little more sense now. Thank you!
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