The very first thing to understand is that to be an inventor you need to have an invention, which means you need more than just a idea. The truth is that you cannot patent or protect a idea or a concept. However it is an undeniable truth that all invention start with a idea, but an idea is something that can be protected by any form intellectual protection. 
So what do you do when you have an idea? How much is required in order to have an invention?
In order to be an inventor the law requires that you contribute to the conception of at least single patent claim in a patent application. This is one of many in patent law where the term used complicated understanding. The “conception” spoken of in the requirement mentioned is not merely a idea, but rather it is much more. The patent law requires that in order for someone to be an inventor, they need to “dominate” the invention by excersing complete mental control over the subject matter of invention, from creating through testing. Thus, the patent law do make a distinction between what we consider an idea to concept as those terms are used in everyday language and “conception”, which is a term of art that has a specific legal definition. So in order to be an inventors you must not only have the idea but also you need to have the know-how with respect to bring the invention into being. Another unique twist is that you do not actually have to bring the invention into being, others can do it, but they must be acting on your direction and under your supervision. This is how the leader of a laboratory who actually does not do testing winds up being inventor.
So what do you do when you have an idea? How much is required in order to have an invention?
It is very difficult, if not impossible to make progress if all you have is the idea and no ability to move forward. That means that the first thing you need to do is embark on research to figure out as much as you can about the problem you are trying to solve and what will be required to solve that problem. As you develop more and more ideas by adding details after details you are marching forward from having a “mere” idea that cannot be protected and towards an invention that can be protected. With an invention the demon is really in detail.
Ultimately when you come to a point where you just cannot go further, and need some additional help from an engineer, scientist etc. The patent law require that in order to file a patent application you need to be able to describe in writing how others could make both make and use the invention, with same level of details as would be required in instruction manual. In order to get help you do not want to give up right to your invention. You will want to have a written agreement in place that will allow you keep ownership of the patent rights if you seek assistance from someone else, whether they are professional or not.
Why having agreement is so important?
Absent an agreement co-inventors will own 100% right to invention. So, your co inventor can do whatever they want and you cannot stop them. If they make money you don’t even have the right to the invention. So your co-inventor can do whatever they want and you cannot stop them. If they make money you don’t even have the right to seek a portion of what they make because they own the whole thing the same you can, at least in the eye of law. So it is absolutely critical that as you proceed from idea to invention that you have appropriate agreements in place to ensure continued cooperation by anyone who might be an inventor and need to be named on patent application.
Frequently people don’t want to ask for agreement or spell out relation in advance, which i suppose is human nature because it happens so frequently. Once money is involved people have a funny way of changing and behaving differently even greedy. So resist temptation to jump right in before agreements are in place that protect you, protect the invention rights and define the relationship between and among collaborators.
