From bash man page:
Arguments
If arguments remain after option processing, and neither the -c nor
the -s option has been supplied, the first argument is assumed to be
the name of a file containing shell commands. If bash is invoked in
this fashion, $0 is set to the name of the file, and the positional
parameters are set to the remaining arguments. Bash reads and executes
commands from this file, then exits. Bash's exit status is the exit
status of the last command executed in the script. If no commands are
executed, the exit status is 0. An attempt is first made to open the
file in the current directory, and, if no file is found, then the
shell searches the directories in PATH for the script.
So the first argument can be referred as $1, the second as $2 (until $9, if more you need to process it in other way such as using shift...)