The default usage is quite simple: ./backup.sh will dump every database that current user can get access to in separate files.
The option list is here:
-u [MYSQL USER] If needed (eg: you're not root), provide login info to mysql.
-p [MYSQL PASSWORD] If needed (eg: you're not root), provide login info to mysql.
-s Same as -p but password will be asked in shell. Ignored if -p is used.
-d [DATABASES NAMES] Backup only provided databases, separated by ','. If not used, script will backup all databases.
-o [OUT PATH] Create path if it doesn't exist. If not used, will backup all in current working directory.
-a Backup all databases without asking for confirmation.
-f Backup information_schema and performance_schema, ignored by default.
-H [MYSQL HOST] Specify mysql host. Default is localhost.
-h Display this dialog.