Dusk is the beginning of darkness in the evening, and occurs after twilight, when the sky generally remains bright and blue. Civil dusk is when the earth has rotated enough that the center of the sun is at 6° below the local horizon. This marks the end of the evening civil twilight, the point where artificial illumination is required to read outside. It can be confused with sunset, which is the point at which the earth has rotated enough, that the sun is no longer visible from the local horizon.
Evening is the period between the late afternoon and night when daylight is decreasing. Though the term is subjective, evening is typically understood to begin before sunset and extend until nightfall, the beginning of night. Evening thus spans the period of twilight, but begins before it and depending on definition may extend past its end.