wt actually jvm do.?
java virtual machine(jvm) is available for different operating systems which converts the compiled bytecodes in to a form that can be understood by that particular operating system. Availabilty of jvm for different operating systenm makes java PLATFORM INDEPENDENT ie we can write a code which can be run on any operating system.
jvm is a java virtual machine help for the run time execution
basically it's a virtual computer running within your computer, when you run a java program it runs inside the jvm, the jvm runs in your computer.
In high level, it's a container that runs your java applications/applets that is encapsulated on its host machine.