I am not sure what exactly you are asking here, as the people on the two sides of a mountain range are not necessarily going to be any different from one another. What I assume you are asking is how their weather is going to be different.
If that is what you are asking, the people on the leeward side of the range will see much less rainfall than those on the windward side. The reason for this is that the mountains will force the air upwards. This air will be relatively full of moisture. As it rises, the moisture will condense and fall. The air that crosses the mountain will be dry.
I have seen this effect most clearly when I lived in Hawaii. O'ahu, for example, has a windward side that is much more rainy and green than its windward side.