For planning What is the best way to visually represent a typical registration flow where a user registers on a registration page, there is then a confirmation page followed by validation email and welcome email, etc?
Flowchart is the most intuitive way to visualize a process. It is common solution any step-by-step instructions. It also allows to highlight important details: main sequence (path), final steps, etc.
Activity diagrams are graphical representations of workflows of stepwise activities and actions1 with support for choice, iteration and concurrency. In the Unified Modeling Language, activity diagrams can be used to describe the business and operational step-by-step workflows of components in a system.
Some useful guidelines:
It depends on the goals of the diagram. For example:
- If the diagram is for empathizing with the user experience, you might want to consider a storyboard or narrative script
- If the diagram is to document feature requirements, a workflow diagram would probably be more appropriate.
- You may also want to consider something like a clickable prototype, which won't visually represent the flow but will interactively represent the flow while visually representing the actual screens.
It's hard to put a label on what that diagram is called but you are essentially looking to visualize the flow. This can be called a 'flowchart', 'user flow', 'UI flow', or a ux 'use case' (different from a programmers 'use case').
A good example of a flowchart can be found here:
And a good article about a quicker way to sketch this out can be found here:
I don't think it really matters what diagram you use, what is important is that you can visualize what needs to be done and get everyone on the same page. I personally prefer a flowchart because it has well defined symbols that create a standardized language to convey the necessary steps for designers, project leaders, programmers, and the likes. Either way, for registration, I think the conditional is an important aspect for showing what decisions the user will have to make and where that will lead them. Also remember that some conditionals will be decided by logic not the user.