Ask for feedback
When you have defined the idea - know that it will change over time. Probably no entrepreneur in the history of the world has known on day 1 exactly what the company would be doing a few years later. The reason for this is that as you move forwards, you come up with new ideas and find better ways to do things. Your future customer will tell you about what they need and step by step, you will develop new products and services over time. You will find easier ways to deliver them and so on.
Based on this, it is important that you start talking with people and show them your Basic Business Plan. Tell them what you want to do. Too many are too focused on keeping their idea a secret - but why? Sure, you don’t have to call your competition to tell them about what you are doing, but if your idea is so secret that you can’t tell anyone about it, then it will be hard to build a business from it. You need to talk about your idea. And you need feedback from people.
Talk to people that you know. Ask them what they think and ask them for ideas and for feedback. You want to validate your idea and you want to make it better and easier to understand.
Let me also warn you: People will tell you things are impossible. Do not fear them. People will tell you things are too difficult or impossible all the time. Probably most people will tell you this and it is part of being an entrepreneurs. Only look for an easier way to explain the idea to them and ignore any negativity you get. When you know, you know.
Also, be careful who you ask for advice. If you can, ask people who have done something similar as to what you want to do. If you want to learn how to fly a plane, you ask a pilot. If you want to know how to build a house, who do you ask? Well, it is the same with building a business. Ask people who have results that prove they know what they are talking about.