환영합니다 vs 어서오세요 - 환영합니다: "Welcome (to a place, group, occasion, etc)!". - 어서오세요: A greeting for someone arriving. Implies "Welcome", "Make yourself at home", "Good you're here", etc. * There is also "잘 오셨어요" which is sort of in between the two in meaning. For informal occasions like one's home or a small gathering, 어서오세요 and 잘 오셨어요 would work better. In more public occasions or to emphasize "welcome", 환영합니다 and 잘 오셨습니다 are probably more appropriate. Generally, 어서오세요 and 잘 오셨어요 sound nicer and warmer than 환영합니다. In your examples, world, house, and group sound more personal, so all three would work fine. For classroom and web page, I think 환영합니다 would work better. These are not strict rules though, and I'm not sure which one might be better for "life".