I have a java project, which runs fine on eclipse. Right now, I need to run it from command prompt, like java classpath ... How to setup this classpath based on the stored ones using in Eclipse.

Read the JDK doc about how to use the java command.

Basically enter:
java CLASSFILENAME

where CLASSFILENAME is the name of the .class file.
If in a package there is more to it than that.

No idea how Eclipse works.

Briefly - make sure any non-standard dependencies (libraries) you may use have been placed somewhere (anywhere) in the classpath, then package the whole of your project's classes and resources into a jar (Eclipse: File -> Export -> Runnable jar file) which you can then run by java -jar myJarFile.jar, or by simply double-clicking it. Easy!

Set up a build file in ant. Put your dependencies in a directory and include them in the jar. Run the build file.