There's a trope among developers of the people that have a "great idea" for an app or website, but no coding skills or knowledge. It's quite common for those people to come to a developer or community looking to find someone interested in putting in the work of creating the thing that they envision. Most of the time it comes as a startup pitch where they expect the developer to put in work with no promise of ever receiving payment. This is basically asking someone to work for free on the gamble that there will one day be more income than the cost of infrastructure. Many developers tend towards a skeptical or cynical reaction towards this. There was even a whole plot point in the show Silicon Valley about it. One developer's reaction can be read here
I'll share with you some of the information that came out in one such conversation.
Think of this like a startup
If you were starting any other type of business than tech you would put together a specific plan before bringing in any other people. Consider "I have an idea for a business" and put effort into modeling out, describing, and planning how your business works and get lots of feedback.
If you had a restaurant idea and went to a chef saying "I have an idea for a restaurant, but I can't cook and I'm looking for someone to handle the kitchen part." You had better have a strong business case for why a chef would want to invest their time in your idea.
There are lots of things that you can plan out without a developer or writing any code at all. You can write the business cases(s), draw out the screens in all sorts of user friendly tools (or on paper), get feedback from potential users about what features they would want, etc.
When you come to the point of sitting down with a developer, then you would be handing over a bunch of specifications and they can just build it. The best way to do this would be to have some amount of money to invest to pay the developer to deliver a some bit of the product, This is exactly like you would do if you were prototyping a physical invention.
More often than not, devs find that when/if they get involved with this type of thing they aren't just developers they're also expected to be designers, marketing, search engine optimization (SEO) experts, and product managers. Suddenly they are doing the work of a whole team (or more) with no promise of ever being paid.
You may very well have an amazing idea and find the perfect developer that both believes in the idea, and has endless free time to devote to it, but keep in mind that what you're asking is basically "I had this idea in the shower that I've put no effort into and I'd love for you to spend all of your spare time building this thing for me so that I might be able to make lots of money without doing anything." If you've put in lots of effort and have a well laid out plan for this company that you are starting, you are much more likely to find a developer that's interested.
Special thanks to George Spake for assisting with this content.