The bash shell can guess what filename or command you are trying to
type and automatically finish typing it for you. Just type the
beginning of a command or filename and press Tab. If bash finds a
single unique completion, it will finish the word and put a space
after it. If it finds multiple possible completions, it will fill
out the part all completions have in common and beep. You can then
enter enough of the word to make it unique and press Tab again. If
it finds no completions, it will simply beep.