changing environmental variables

hi i don't know anything about running java, but there is a new program under development that i had got off the net. it is called videothen , you hyave got to go to your enviroment variables and you have to edit the .bat file and change the cd command to point to your videothen directory.
cd c:\videothen

for example.

also the java.exe must be in your PATH and the classpath environment variable must point to the jre directory. you can change the PATH variable (and add CLASSPATH) by going to controlpanel->System->Advanced->environmentvariables

is there any help someone can give me. i can follow directions. how do you direct your path, and put your classpath environment variable in your path. i have the java jre installed i think, but i don't know what to put in the environment variable to make it all work