It's not a rar, it's a jar and there's no need to extract it. What you have to do, is to add it to the classpath. When using the command line, this is done via java -cp <your-jar>;<another-jar>...
When using an editor/IDE, there should be an option to add jars to the project somewhere. One you've added the jpct.jar, do the same with the jars that exist in the lwjgl-subdir if you want to use OpenGL. You also have to add the native parts of LWJGL by setting the java.library.path to the directory that contains them. Again, on the command line this is done via -Djava.library.path=<your-dir>. Your editor may have a similar option.