Hip hop is a form of musical expression and artistic culture that originated in African-American communities during the late 1970s in New York City. DJ Afrika Bambaataa outlined the five pillars of hip hop culture: rapping MCing, DJing, breaking and graffiti writing. Since its emergence in the South Bronx, hip hop culture has spread around the world. Hip hop music first emerged with disc jockeys creating rhythmic beats by looping breaks (small portions of songs emphasizing a percussive pattern) on two turntables. This was later accompanied by "rap”.
Contemporary R&B (also known as simply R&B) is a music genre that combines elements of hip hop, soul, R&B and funk. Although the abbreviation “R&B” originates from traditional rhythm and blues music, today the term R&B is most often used to describe a style of African American music originating after the demise of disco in the 1980s. Some sources refer to the style as urban contemporary (the name of the radio format that plays hip hop and contemporary R&B).
Please see Wikipedia for more info on hip hop and R&B music.