Very ignorant on the Japan issue with radiation can someone help me please?

hi so right now i'm just going to put it out their i'm not educated on this whole issue of Japan at all but i know Japan isn't dreadfully covered all the way in radiation i mean i think its still safe to go to Japan. I believe it is but can someone explain and help me understand the radiation leakage in Japan right now and why so many people are leaving ? and does the radiation effect all of Japan? like Tokyo, Hokkaido, Kyoto or is it safe to live in these places without effects? i'm sorry i'm just really confused and i like to know about it.