Pretty overwhelming isn't it?
Really, the only thing you will need is:
something like noteworthy composer $15.
Noteworthy makes midi music only. That sucks, but here you will learn what the different notes mean, what sharp/flat means, the different between slurring notes together and not, and many many more things. You get to experiment right away even without a keyboard. I think there's a free version on there too. You can experiment with the different midi instruments provided to try to get a different sound. This is how I started. I did have access to a cheap keyboard ($30) and I practiced finger movements.
The bigger Digital Audio Workstations(DAW) are very very complicated and overwhelming at first. I recommend that when you are no longer content with making songs in Noteworthy to give FL studio a shot. It is primarily structured around making techno songs, but if you keep at it long enough you will learn the arts and be able to make any type of music with it. It is one of the cheaper options for a DAW being priced at somewhere around $100. If you make it this far, pick up a midi keyboard that has a midi in/out and grab one of these
The converter transmits the state of key presses/releases to your computer so you can start getting into the groove a little better while composing music. I remember being blown away when the studio recorded my input for the first time.
The DAW hurdle is one that will take a long... long time to learn your first time. There are many aspects to composing music that will upset you and you may end up taking a break. But it will always be waiting for you to return.