(answered above in the comments already. It was suggested to submit this as an answer after the question was re-opened.)

You start with a problem - something you want to solve - no matter how complex you think it is. Then you take this problem and you write it down and start to break it into smaller problems. You then break down those smaller problems, etc. until you have something primitive that you already know how to solve or can do so with some effort. You start coding each of these pieces and organize them into different functions or different classes, etc.

Then you work on the next sub-problem. As you are working on each problem you can write small test cases and actually see you progress coming into fruition. There will always be challenges along the way, but at no point will see it as something too colossal to even approach (what are seem to be dealing with now). This is true for programming and many of life's challenges. They key is to break it up.

As for what to do - the idea. You can try to invent something new, but you can also take something that you might have a passion for and already exists, but just make it better or even just different. I'm currently writing a guitar tuner app for Android in my spare time. I know there already exist many other guitar tuner apps, but I thought this would be a fun and challenging project so I took it on. At first it seemed almost impossible, but after I broke the problem into smaller steps it's actually coming together nicely. Divide and conquer and be persistent with your goals.