If you're looking for playing rules, to view the on-line version of the high school rule book, you need to be a registered official, coach or school administrator.
High school games in Ohio (and most states) are played under "National Federation of State High School Associations" (NFHS, or FED, for short). These rules are available to registered members on the NFHS website. They also sell rule books to the general public and that information is on their website as well.
The OHSAA does not publish their own playing rules. They do make a small number of modifications to the standard NFHS rule book, for instance the 10-run mercy rule and rules governing protests or suspended games. But for the most part, the games are played under by-the-book NFHS rules.
The main function of the OHSAA is that of player eligibility and participation.