All US states require that their teachers go through a certification process for everyone that will be involved in teaching children from pre-school through the 12th grade. This process is intended to improve the over quality of education. Due to the substantial shortage of teachers in this country, many states also provide an additional method to get certified known as alternative teacher certification. This is a temporary way to get certified.
Most states have reciprocity agreements with other states, so if you are certified in one state you should be able to get authorization to teach in these other states. Many schools offer degree programs that are designed to aid you in getting certified. In some cases, the schools incorporate certification programs as part of the curriculum.
There is a severe shortage of qualified teachers in the US. The demand is fueled by many sources, including the more demanding standards and the requirement for those who are certified.