Based on the app’s objective, can develop a wireframe prototype that shows how the end-user interacts with the app and its ease of use. The purpose is to quickly see the navigational flow and page layout to enhance user experience. Page layout covers the placement of each element. Consider this the skeleton.
Designing the interface, dressing the skeleton up. Custom designed icons and other elements will adhere to the branding rules and the app’s purpose.
Adobe Illustrator and Figma (Working knowledge)