I can't really tell what you are doing. What part of the process is this happening at? After you've edited all your footage into the timeline? When you say "finalize", are you talking about the process of finishing the footage in the camera, or are you referring to exporting the final movie? What file format are the movies getting imported as? Are you looking under the Share menu to find all the different export options?
This is really one of those things that's much easier to understand visually. It's really hard for me to imagine what exactly your problem is without seeing what you're actually doing. It sounds like you might have skipped a step somewhere, because I think you have to export the project as a movie file before you can create a YouTube or another version. Did you watch or ready any tutorials before you started?
If you're near an Apple Store, I would sign up for one of their free instructional seminars. There is probably one for iMovie.
Here is a series of iMovie tutorials on the Apple site. These are almost always a good place to start if you're new to Macs. In fact, one of them is specifically about exporting for YouTube.
Apple - Find Out How - Movies - iMovie
Also, try looking in the Help menu in iMovie. There's a lot of information there too.