How to work with Facebook Online Schema Change?

Question

PHP

Actually, it is required to add an index on a very large table. The option in the forehead does not work, because in fact it paralyzes the work of the database on the production server.
I'm looking in the direction of Facebook Online Schema Change, but I don't fully understand how to launch it.
An example is in the readme:

#php osc_wrapper.php --mode=statement --ddl_file=create.sql --dbname=production

In this case, osc_wrapper will read in ALTER or CREATE statements from a file create.sql and then attempt to alter the schema of tables in production schema.

Do I understand correctly that I need to put the necessary ALTER query in create.sql and execute the above command from the console?