One of the most prominent functions of the UX designer is to construct flows. Paths that users follow to execute their tasks and ultimately achieving their goal.
Flow Modeling helps to explore back and forth actions in the context of an app, website, or SaaS platform. It does not necessarily explore interface layout and elements positions. But, flows modeling focused on validating concepts by stitching together isolated next and previous steps while linking navigational points. At the same time, it is a tool to see if the user or visitor can reconstruct the followed path in his mind. On the subconscious level, people search for relay points: "How I got here? What is waiting for me next? How do I reach the starting point?".
Designer's task is to create a complete picture that involves both logic and feelings in the flow. There are several ways how to do that. Information Architecture maps, usually, about drawing boxes connected with lines, and this helps to outline preliminary navigational logic. Where Scenarios are about sketching scenes and elements later building a sequence like for a movie. Such scripts capture characters (personas) and feelings, helping to define wins and wow effects. In both cases, exploring negative experiences or dead ends is also part of the flow.
Good design, in this case, rely on the observation of people in the real world and creating flows that are reducing work and effort in the digital solution. It doesn't make sense to introduce something in an app that takes more effort than takes in real life. For example, taking paper and writing an address is much faster than to fill in an address form on a mobile device. It is a tremendous hassle to write a postal address in multiple fields, especially if autosuggest is not available. As a good example, Google Maps employs seamless flow in finding a street from one input filed and suggesting to navigate to the address as the next step. That in comparison to a printed map is a great win.
UX designer is responsible for drafting and testing interactions along with the flow. It can be in the form of logic maps or navigational prototype. Quick testing (observation) is playing a significant role in Flow Modeling. Just because predicting people is very hard, using the techniques helps to explore overall logic, expectations, and feelings.