We've been focusing on the User Experience (UX) of our product.
UX is a critical skill to build as a designer. It focuses on answering the "why : how it works " of building a specific product. Mastery of UX skills will yield a high impact on the products.
But now let’s move on the "how it looks". The User Interface (UI) is how to solve the problems we know we need based on our UX research. The UI we're describing assumes we're building a digital software product. It focuses on layouts, pixels, and user flows.
UI is also important to building successful products, as without it users will not enjoy what you build.
In practice as a designer, you'll often find yourself gravitating towards UX or UI depending on your skills, interest, and your team's needs. However, in many companies, you'll find these roles are blurred together into a UX/UI designer who is responsible for the total user experience.
vs. Visual (Graphic) Design
UI, UX and Graphic Design are all interrelated, yet not exactly synonyms of each other. The UI Designer helps build digital user interfaces, as well as helping to create style guides and design systems. UX Designers focus more on the holistic experience, solving problems, designing the right user flow, and focusing on user delight. Visual (Graphic) Designers, originally from the print industry, focus on how things will look, including items like icons, colors, fonts, etc.