(in a nutshell version)
Flashing your bios usually means downloading a flash program and a bios code for your particular M.B./bios. You should go to your Motherboard manufacturers website for exact instructions on the flash (programming) procedure for your particular board. It can be very specific.
One way is to add these files to a bootable floppy disk and booting with it, starting the flash program, saving your old bios code (in case something goes wrong) then flashing the updated code into the bios chip. (better hope the power doesn't go off as any interuption can hose your computer) The bios chip is able to be programmed (flashed) with new updated code, giving you possibly new features, bug fixes ect.
Revision 1.XX is the current revision or version of your motherboard. We can hope that each subsequent revision will have added features and or stability than a previous revision.