Well it seems like you successfully built the hello world demo, and as you indicate you found the files in WORKDIR. But that's all a package recipe does. It builds a package. You need to tell your image recipe to include your new package in the final image. You can "cheat" and put those instructions into your local.conf file, using something like:
IMAGE_INSTALL_append += " hello"
However beware that this technique only works if you are using a standard image recipe based on image.bbclass.
Better yet, modify the image recipe you are using in a custom layer of your own creation, and add the package in an image .bbappend.
For example, if you are using core-image-base, create your own custom layer and create a core-image-base.bbappend in that layer, and inside that bbappend, add the dependency for your newly created "hello" package.
There are many examples in the metadata. Take a look at core-image-base.bb and image.bbclass to get some clues how images are created. Take a look at any packagegroup-core*.bb for examples of how to specify your "hello" world as a runtime dependency so that the package gets installed in your image.
Note also that the Yocto Project has a mailing list with lots of friendly folks on it, and would be happy to answer your questions. There is also #yocto and #oe on freenode.net. Check out yoctoproject.org for specifics.
Hope this helps.