You could choose the name of Database, the name of User, AS YOU WANT.
You need to create Database and User BEFORE launching install.php, and you will supply your choice when asked for Database identification (informations saved in 'dbconfig.inc.php' for ocsreports). Also you need to set Database indentification in Apache conf file 'z-ocsinventory-server.conf' (for ocsinventory).
For example, you can name Database as 'ocsweb', User as 'ocsuser' (not 'ocs'), and also do 'flush privileges'.
So, except User name 'ocs', the doc is complete and correct.
(If you name the User 'ocs', you will get a message on web interface ...)
IMHO I suggest to learn some basics of MySQL/MariaDB administration : creation of databases, creation of users, access rights on databases for users, save and restoration of databases, some hints of MySQL/MariaDB configuration (mysql_secure_installation, bind, ...)