Let's see, -whenever you use "since" in english, you must use "desde/desde que" in spanish: I live in NY since I was young/since 1985: Vivo en NY DESDE QUE era joven/DESDE 1985. - whenever you use "FOR" in the sense of a period of time from a certain moment in the past up to the present, then, in spanish you have to use DESDE HACE: I've been living in NY FOR 10 years: Vivo en NY DESDE HACE 10 años. Whenever you use in english the word AGO, you have to use HACE in spanish, but, attention, the structure of the sentence varies a little: He died ten years AGO: Murió HACE diez años. She told me that two days AGO: Me lo contó HACE dos días.

Hello my friend. Ok, I will explain you. You use "desde" if after there is a year, for example: "Vivo en los Estados Unidos desde 2010"; in this case, you even live in this country. "Desde hace" is when you say the years in numbers, ex: "Vivo en los Estados Unidos desde hace dos años" in this case, you even live in this country too. "Hace" is used in the same form mentioned before. :D