There are no special classes to take to be a psych nurse. As long as you have a license, you can nurse on a psych floor.
When I was in school, I worked as a nurse tech at an area hospital that had a psych unit and I asked to be based on that floor but the supervisors would not do that. I did get to go to the psych floor about 50% of the time though. That was the best way to learn. Better than clinicals, better than books, better than advice from friends. I had many people try to discourage me from working there (even as a tech) but I loved it. I got to shadow staff and see what psych nursing is really all about.
I would also recommend if possible to work at a large teaching hospital so you see a variety of psych patients and the latest psych meds. People who work there are used to everyone asking questions so you get to learn a lot and the pay is usually better. I have many psych nurse friends who have worked for small for profit hospitals and they have always complained about unsafe staff
atient ratios. Adult psych is my fav. Working with kids is too physical. Kids like to fight. Adults for the most part are aware that there are legal consequences for violence so they are usually not as labile.
In Ohio, psych nursing is not considered a specialty which rates higher pay. I have my certification in mental health/psych nursing and many places will pay higher wages for that. I would check with your school as they will probably have stats on latest pay rates for new grads for your area. It differs greatly from region to region.