I still use the runbuild.bat (command line) when I update my game on Steam because it's just so easy. You copy the contents of your game into a specific folder and run the .bat file.
For a first time release, most of the original Steam video tutorials are a little outdated, but still useful.
I just found a recent video using the GUI to upload the builds:
The Steamworks App and Store Admin pages are pretty self-explanatory and easy to set up. However, there are a lot of graphical elements you'll need to create.
Don't forget to create trading cards and emoticons as well. Many players will buy your game for that alone (if it's cheap enough).
PSY