Scan stitching is a part of the DFT(Design For Testability) process. Flipflops which pass the DFT DRCs will be converted into equivalent Scan cells(like MUXed scan/LSSD/clocked Scan). These scan cells will be connected serially when you stitch the scan chain. The scan chain will act just like a serial shift registers in scan mode.
And for RTL c0mplier command you can always browse through the rc_command_reference pdf.