[U-Boot] Internal Boot mode

Can anybody tell what all happens inside an i.mx6 board when we try to boot it in internal mode? Is it that in internal mode the board does not look into the flash at all to discover the u-boot image and the image must be provided only from the serial port? If yes then what steps should be followed to perform internal booting? It would be of great help if commands for performing internal booting is provided.

Thanks in Advance!