Radio City Music Hall is in the Rockefeller Center complex. Depending on where you're coming from, and how far you are willing to walk, you can take the 1, 2, 3, line, the 4, 5, 6 line, the B, D, F, V line or the 7 train.
Take the subway. You can go directly from one to the other in just a few stops: take the Downtown B-D-F-M (the orange line) from 47th-50th Street-Rockefeller Center to 34th Street-Herald Square (at...
The address is 1260 Avenue of the Americas (another name for 6th Avenue is "Avenue of the Americas"). It is on the corner of West 50th Street and 6th Avenue.