mack:
Most train stations are housed in a huge building or connecting buildings where you can get off one train, go downstairs and go up another stairs or downstairs to another numbered platform for your connecting train. Shinkansens are close to each other but away from local trains.
You may need to walk further if you're connecting between local trains and Shinkansens. There are a lot of signs directing you to the various train lines and platform numbers including where the Shinkansens are. The signage are similar to airports with clear directions.
In addition, there are overhead lit signs in Japanese and English announcing the name of the trains, their respective platform, the destination and departure times. You can also ask any train station personnel at any gate for direction by showing your ticket. Don't hesitate to do this.
Since you're new at this, you should allow about 20 – 30 minutes for transfer to your next train. This should give you relaxed time so that you don't rush walk in the wrong direction. I've traveled with JR trains a number of times but still give myself about 15 – 20 minutes transfer time although for some I had only about 5 to 10 minutes. If not, the next train may be an hour or more later.
Make sure you're on the correct platform. The Shinkansen trains are almost always on schedule to the minute. So, if you're on the designed platform 15 minutes early and there's a train at the platform, do not go on that train. Look at the overhead lit sign to make sure your train appears. Look at your ticket for the name of the train, CAR NUMBER, seat number and departure time. Then, look on the platform floor at the edge next to the track for the train name such as HIKARI and the car number that matches your ticket to know where you should wait. I highly recommend that you show your ticket to ANY of the station personnel on the platform to confirm that you're at the right place.
To search for JR trains, go to
http://grace.hyperdia.com/cgi-english/hyperWeb.cgior you can go to
http://www.japanrail.com/JR_hyperdia.html where the first page will explain how to use the train's website. For JR Rail Pass users, select the Shinkansen and Limited Express while putting a check mark in the Except NOZUMI block.
If you're traveling a long distance such as from Tokyo to Aomori and there's a train change in Hachinohe with only 6 minutes transfer time, split your train search if you're not comfortable with the short transfer time. The first will be from Tokyo to Hachinohe. The second search will be from Hachinohe to Aomori. Then you can decide if you'll go with the 8 minutes transfer time or wait for the next. In this case, it only takes about 1 – 2 minutes to get to the next platform so the 8 minutes transfer time works.
As long as you give yourself enough time and you remain calm, train travel is not difficult and is fairly easy to do.