The 74HC595 is an 8-bit serial-in, serial or parallel-out shift register with a storage register and 3-state outputs. The shift register and storage register have separate clocks, allowing data to be shifted in while maintaining the current output state.
Multiple devices can be cascaded by connecting QH to the SER input of the next chip. Data is shifted in on the rising edge of SRCLK and transferred to the output register on the rising edge of RCLK.