What do you get with Japan Rail Pass?

Hello! My friends and I are traveling to Japan this October. We have heard from some people that it is good to buy Japan Rail Pass, others tell us that it is not necessary to buy it cause we will have to pay extra for some trips although we have it. Can you tell us what would be the best thing to do and what do we get with it?

Japan Rail Pass is quite useful. It is a discount ticket that allows unlimited rail travel throughout Japan over a period of 7, 14 or 21 consecutive days. There are two versions: ordinary (coach) class ad green (first) class rail pass. It is possible to travel almost anywhere in Japan by train. The pass can provide you with some savings but there are also some restrictions. These restrictions do not apply to date and season. Almost all trains operated by the Japan Railways group are included in the rail pass. The Japan Rail Pass doesnt cover Nozomi-type Shinkansen bullet trains on the Tokaido/Sanyo lines. If you want to use this train you will have to pay the full price.