A persona is a fictional character profile based on the patterns you discovered in your research. It turns "the user" into a tangible person.
Before we start, let's clarify a frequent source of confusion: UI vs. UX. It's similar to having an understanding of the difference between a car's engine and its dashboard. Both are necessary for a pleasant ride, but they have very distinct functions.
Think of UX like the building architecture. You don't always realize it when it's good, but you certainly notice when it's bad. UX design is concerned with the overall feel of the experience. It is concerned with:
If UX is the architecture, UI is the interior design—it's all that you can see, touch, and click on. While UX specifies the "what" and "why," UI deals with the "how it looks and feels." These are:
A product must win both. Excellent UX with bad UI is usable but not nice. Excellent UI with bad UX is stunning but not useable. The aim is to win both: a product that performs well and is awesome-looking.