Complex sentence: Slap bass was used by Western Swing and Hillbilly Boogie musicians, and became an important component of an early form of rock and roll that combined blues and what was then called hillbilly music--a musical style now referred to as rockabilly.
Split into simpler sentences: Slap bass was used by Western Swing and Hillbilly Boogie musicians. It became an important component of an early form of rock and roll that combined blues and what was then called hillbilly music--a musical style now referred to as rockabilly.