There are two ways to go about this... you can start on a PC or on a real keyboard.
If you start on a PC, you should familiarize yourself with software that produces MIDI music... right now Guitar Pro is the most feature-rich but at the same time newbie-friendly offer available. But mind you, you will need to familiarize yourself with music theory, there's no way around it. Luckily, you can learn it by persistence and experimentation, if you have some talent for music.
You could start with loop-based music software like FL Studio, but you will be wasting your time. You will see results but won't exactly be learning anything. In the long run, it's not worth it.
If you want to start on a keyboard, you will need a VST bridge software like ProTools and the like... I personally use Cubase, which not only is very rich in features, but also has a kick-ass student edition that won't leave your pockets empty.
Then read books and tutorials... many, many of them.