What the heck is a visa? Why do I need one? How do I get one?
A visa is an endorsement placed within a passport that grants the holder officer permission to enter, leave or stay within a country for a specified period of time. Many countries (ie European Union) grant American citizens automatic visas when they enter for a specific amount of time. However, if you are staying in the country for an extended period of time, you will likely need to apply for a visa.
To check visa requirements, you can go to the embassy website for the country you want to intern in. It will be important to know the timeline of your program.
The embassy should also have instructions on how to apply for the visa. If you have already secured an internship, check with your company for any information regarding the necessary visa for your position. They may even do the process for you.