First of all, putting all your code (java files) in the bin directory of your JDK is NOT a good idea. Create a special directory for your poject somewhere, lets say c:\myproject. Then put all .java files in c:\myproject\src. If you put a Java class in a package (package com.myproject.blabla as first line in your class) then you need to create the package directory structure inside the src-dir. (would be c:\myproject\src\com\myproject\blabla in the given example).
To be able to run javac and java from your project directory, you need to put the bin directory of your JDK in your path. In a prompt you put: set PATH=%PATH%;c:\yourJDKdir\bin
Then you can call javac and java from within your project directory, pointing to the source files in the src dir, en maybe putting the class files in another dir (build) next to the src dir. Use javac -help for the syntaxt for this...
The classpath is where you need to put the things the compiler en jvm need to run. So if things don't work (class not found errors) put your src dir in the classpath.