friends me ne bohat sare bootable usb se mutaliq threads dekhe hen

to mujhe ye maoloom karna he ke bootable usb se kya murad he or is se kia faida hosakta he or agar usb ko bootable banadya jae to kia is ka usual useg b hota he yan as data deliver etc

plz assaan or a.b,c se guid ke jea ga