I'm not sure I understand exactly what your issue is but i'll try to answer. You can store your photos anywhere you'd like including an external hard drive. The key is when you import the photos into lightroom you have to "tell" it where the photos are. When you begin the import process on the right side of the import screen you set the destination for the import. You can set either your internal hard drive or an external hard drive as your location as long as you do this at the time of import. If you choose an external drive the photos do not have to be placed on your internal drive first. In addition, your lightroom catalog(record of edits, not the photos themselves), can be stored either on your internal HD or external HD.
Thank you...If I am getting an error message when trying to do this does this mean that my EHD is not Mac Formatted....With that being said how do i move those photos from my internal hard drive to my EHD. You were exactly correct on what I was getting at..I was pretty sure I could go directly from camera/SD card to EHD.
The drive will need to be formatted for mac. You can reformat yourself using disk utility(google for how) or buy a disc pre-formatted for mac. As far as moving files from internal drive to EHD, take your folder with all your photos and drag directly onto your EHD. You will need to direct LR on where these images are the next time you open LR.