Read the JDK installation instructions. In step 4 ("Update the PATH variable") you'll learn how to set an environment variable. Setting JAVA_HOME or J2EE_HOME goes the same way as setting PATH.
The thing is...nobody CAN tell you exactly what to type. When you installed it, you could have installed it ANYWHERE. Without knowing where YOU installed it, it is impossible to tell you what to set your environment variable to.
The environment variable is used by your OS to know where to find your java install. So you have to set it to the correct value for where you put it when you installed it.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Try a search for java.exe which is an "every kind of file", that might give you a hint for your path. Remember the path entry starts with the drive letter (eg C:) and ends with "bin".