A developer account is free. You need to grab Xcode if you don't already have it.
https://itunes.apple.com/us/app/xcode/id497799835?mt=12
If you want to release on the iOS App Store or the Mac App Store you will have to pay however you can build & distribute apps with a free account outside of the Mac App Store.
I'm afraid making an application isn't a simple process, do you have any coding experience at all?
Have you ever used tools like Xcode to build an app?
The documentation is probably not the best place to start, you need to get to grips with some of Xcode's UI first.
There are many totorials around to get started, but you need to keep trying until it starts making sence.
Xcode also changes so you need to work out what version you have & what version the tutorial is…
Here is a menulet tutorial for Xcode 3!
http://www.sonsothunder.com/devres/revolution/tutorials/StatusMenu.html
Hopefully a developer will see the thread and offer up some newer tutorials.