@Ka***
on a year-long, multi-entry Non-Immigrant Type O-A visa you will get stamped in for a year once you arrive. The visa is unlimited entries/exits for the validity of it (a year from the date it's issued) and every entry gets you stamped in for another new year..
By exiting and re-entering the country just prior to the "enter before" date on the visa itself you'll get stamped in for another whole year meaning you can get almost TWO years of stay out of that one year visa.
Once you're here, depending on where it is you're going to live. You might be required to file a TM.30 (alien in residence form at the immigration office AND if you're here 90 days you will be required to file a TM.47 (90 day report) every 90 days. BOTH are free to do