I am a backend engineer, I am just trying to understand the process of building a large mobile app.

I have an idea, I gathered all business requirements and I I have used Figma to create a mockup.

I understand that we need 4 steps (1) create a mockup and the story (2) create design and assets and then (3) build web app (4) build backend to capture interaction and store data.

If you collaborate with someone who would create design and assets, do you need to ask for specific formats?. what kind of tools do you usually use when you collaborate with designers?. what do they usually offer (PSD templates, or HTML templates?). I am trying to add different persona and themes, so we need different 3d and design assets.

Could you please recommend a specific guide/tutorials, or share your experience on how you collaborated with designers to build large apps as a team?.