If you're looking for a little bit of language and culture experience for the first time, I definitely recommend Langubridge.
Since I went through the Tokyo E program, that is mostly what my review will be about. If you are wondering about how to begin applying, you have to sign up and pay 85 dollar for the sign up fee and then they will send you all the application materials. The application is quite simple, fill in your basic info, write a paragraph about yourself, add your preferences for your host family, get two recommendations, and email/mail it. After that, you will receive an email about an interview, and most likely it will be a video chat interview through google. You learn more about Langubridge there and you can have a parent(s) present to ask questions if needed.
If it is your first time abroad and you do not know a lot of Japanese, then I really recommend going through the Tokyo E program. They provided a lot of support and very organized activity, you will not feel lost or anything because they are there to help and the home stay families are very well prepared.
They send us pre-departure guides before we arrive to Japan and those are VERY helpful: it includes possible gifts you could give, what happens when you are at the airport, what to expect when you get there, basic phrases, etc.
The Tokyo A, B, and C programs, I would say, are for older, advanced students who know more Japanese, have probably studied abroad before, and want more free time. From what I see, I think the Tokyo E program is like a High School schedule where you have set classes and a set routine. You wake up, eat breakfast, take the train to school, attend classes, eat lunch, attend class, and then take the train back home to spend the rest of your time with your home stay family. The only time to your self is probably at night. You occasionally get homework, but it is not meant to be burdensome like school, so homework is pretty easy. If you are dorming, I think you probably would not have to worry about an early curfew like you have to do with a host family and would not have to return straight home.
Once you receive your host family information, do not be afraid to contact them about living arrangements or if you want to do anything in advance so they can plan for it. Ask them what they have planned for you so you can help them plan things you want to do. I regret not contacting them, therefore I often just stayed home with my home stay family and did not get to experience as much as I wanted/could have; of course we went out on weekends though. Bring lots of spending money, you will be tempted to try lots of food and buy lots of things. I think $300-$500 would be just about you need, as long as you are not a huge spender.
The classes were held in the LABO building, located in Shinjuku. You are divided up into two groups, beginner and more advanced Japanese class. One sad thing is that once divided, you will not be able to interact much with the other class because you have different activities. The classes are quite enjoyable and helpful. The beginner class I took was quite helpful with teaching us basic phrases, sentences, words, hiragana, and katakana.
There are these things called LABO parties and they are super fun. My host family only took me to one, but it was super fun. Depending on your LABO group, you could meet other Japanese students your age or younger or older. Unfortunately for me, I did not go to a LABO party where there were other teens my age, but it was still super fun. The age group ranges a lot and each LABO party-group has different amount of people. There could be 10 in one group and 30 in another. You will learn more about what LABO is on the second day of coming to Japan.
The home stay families are all very nice and well prepared. You may end up with a family that speaks a lot of english, or one that speaks very little. Either way, the houses are very nice and comfortable and the families are welcoming. It helps to know/speak Japanese so you can bond with your family more, but since I could not speak much Japanese, I could not talk to my host family as much as I wished I could have. If you have any more questions, please feel free to email me any time. Oh, remember to take lots of photos! & vlog if you can, even if you feel weird, you will regret not capturing the moment later, so do it!