These are the 3 most important first steps (all are related to validating your idea - meaning checking that there truly is a need for it):
1. Online research with D"r Google :-).
2. Offline research: ask as many people as possible what they think of "the" idea. Not YOUR idea. You need to ask them in a way that allows them to give honest feedback and the only way to do that is either by telling them it is someone else's idea ("my friend has this idea and he wants me to join him...") or by criticizing it yourself so they too feel comfortable to do so.
3. Validation: create a very initial working version and test the waters. read more about this here: https://clarity.fm/questions/6423/how-do-you-do-market-research
It is crucial that you do the above before spending a lot of time and money on an idea.
Feel free to reach out if you need more help.