How best to arrange an agreement with a partner?

Recently (yesterday, to be precise), I began work on a personal project that, in my opinion, has great potential. Since the money (as is often the case) for that part of the project that I myself can’t do, doesn’t delay the pocket, there’s a need for a partner who would agree to work first for the idea, and then for the share. And, accordingly, the question came up - you can, of course, agree “in a friendly way”, but, reading publications on this topic on Habré, I realized that it’s better to somehow formalize the relationship.
The question is how ? A big request from experienced people to advise how to be


PS By the way, are there any artists who can draw icons? ;) Not for the site and not for the application, but, let's say, some abstract icons. If suddenly there is an interested person, you are welcome to drop something in private.
PPS Turbomilk is, of course, cool, but ...