Software Development Process

So I've been reading a few wikipedia articles ( namely this one, and that one ) about software development planning. For it has always been a problem for me, I never finish any project I start because I have no plan to stick to and always find that I can do "that part" in another way and want to re-write the whole thing. 


Now, things will be different. After those articles I managed to grab the essential of the concept of making a plan and sticking to it and not jumping to the implementation process too soon. And so I have chosen the waterfall model for my process.

So I am now jumping into the "Planning the requirements and specs" stage. What purpose will my game serve? Whats the point of it ? I will make a post about this stage when I am done or simply to update.