How can I get a mathematics teaching appointment in Europe or USA?

In the U.S.A. you would need to contact the Department of Education in the state you'd like to teach in and find out if you would qualify to be a certified teacher.  Many states require teachers to pass an exam such as the PRAXIS before they can be certified to teach in that state.  The DOE for that state should also be able to help you with finding a teaching job.
Is there something in Ghana that is similar to our Peace Corps?  It allows people to go to other countries to teach or do other things for a year or two.

There is a need for good mathematics teachers in the U.S., but you can't work here unless you get an appropriate visa first.  The problem would not be in finding a job, but in getting a green card (permission to work in the U.S.).

In the USA, you must have a B.A. in Education and at least minor in a particular subject that you want to teach in if a special discipline such as science or math.  You also must have a teacher certification or Licensure, which varies from state to state.  You would need to know which state you want to teach in and then determine their specific requirements.  As for teaching in Europe, I am not as well versed, however, your credentials should be similar with the difference being what your A Levels, O Levels, etc., are like and any specific qualifications training you might need in a given country....also, keep in mind, what language the school will allow you to teach in.  Go0d Lvck.