*note, this is a broad-based guide to the design process, make sure to google steps that you need more details on!
Below are a list of design resources that are helpful in taking a deeper dive into design! The guide is no means a comprehensive list, and is always evolving.
User Interface is what people see, oftentimes user interface designers focus more on the visual interface and the experience working with these digital visual interfaces.
User Experience is more focused on the user research aspect and implementing the results from user testing a product. The product can be any kind of experience → digital, physical, spatial and more.
Product is focused on the product ideation aspect in response to a problem gained from user research. Aspects of product design include cross-referencing products and tuning into the user groups to optimize a solution. It's brainstorming the solution (app, service, etc) that would solve the problem for the user.
Most designers are called Product Designers or UI/UX Designers which essentially cover the same sphere.
A very abridged version: user research → problem statement → brainstorming solutions → prototyping → user testing → iterate
User research is where designers speak with the user group, or even client, on their needs and specifications. It's an extra bonus to talk to the users of the product in addition to the client, as they might have some unknown insights
Typically, designers can user interview 3-5 people. It's important that these people are all different personas, and can be different in demographic, age group as well as having different use cases for the product.