Smoking laws in Germany?

im going to Germany soon (im 18) and like i know i can go and buy cigars/cigs/and tobbacco. But im unsure on where i can smoke them. is in public okay? like walking down the street with a cig. is that okay? or is there zone for smoking in public. What about in resturants? is there a section or no go all together. Bars? dance/night clubs? also im going to north west phalia