Bethesda currently has an ongoing series of tutorial videos for Skyrim's Creation Kit. These videos cover various subjects, such as building interiors, placing objects, adding enemies to the world and more. If you would like to start modding Skyrim, these tutorials are a good place to start!
The other episodes can be found here:
Once you have successfully created a mod you can use our packager to pack it up and then upload it to SkyrimForge to make it available for everyone.