Um, race is a biological term for an independent species. meaning that different races can not breed and have offspring ( fish and a giraffe e.g.) an ethnic group is essentially what we wrongfully call as 'race'. so, there is only one human race that is divided by appearance ONLY. generically we are identical ( Chinese with a Swedish can have babies). race is a myth, or wrong word even, for an imagined concept that is false. we are 100% not different from other ethnic groups, accept appearance. that difference is due to living in various climates and our bodies learner to adjust to those geographic regions. for example, a black African has evolved so that he can survive the climate of the African continent. vice versa a human from Iceland looks far different because the climate those ancestors had to adapt were much different then those in Africa. hope that explains. ask if some questions come up.
Race is real in that people from different areas of the planet have distinctive features which set them apart... it is myth in that at the genetic level we are all nearly identical, the tiny fraction that accounts for our race is negligible. Ethnicity is the country/area you come from... so someone who is (race) Asian... would also be (ethnic) Japanese or (race) caucasian could be (ethnic) German, French, Scandinavian etc.. :)
Race is a social concept, not a scientific one. From a scientific point of view there is no difference between races: the intraracial differences are greater than interracial differences. As for ethnicity, it's even a less specified concept. It's more societal and cultural, like your language, religion, and other aspects of culture.