teaching as a private tutor

Hello, I live in the USA and I have a four year degree. I would like to teach English in Japan as a private tutor rather than in a school. Am I first required to work for a school before I can teach as a private tutor? Or can I simply move to Japan unemployed and fill out the Teacher Sign-Up form on findateacher.net and then I have students showing up at my place? Also will I be able to get a work visa before I leave the US if I am planning to teach as a freelance tutor? Or are visas only issued to those who are employed by schools?

You can't get a working visa without an employer (school or company) to sponsor you (you also need to fulfill the other requirements for the visa- do you have a bachelor's degree?). This is partly because Japan Immigration wants you to have a guaranteed income, which you won't have with private students, particularly not on first arriving in Japan.

Once you have the visa you can start teaching private students on the side if you want to. Be aware that it takes quite a lot of time and effort to build up a base of private students that will come anywhere near to paying for your basic living costs- don't expect to be able to support yourself just through private students until you have been in Japan for quite a while.

Most students will not want to "show up at your place" or have you come to their house- many people teach in cafes. Nor will it be as easy as that- you will have to put in quite a lot of effort to find a reasonable number of students to teach.