I am not sure what type of workflow diagram standard I should be using to convey the flow of how web application would work to a non-technical and technical person.
Because for myself, as a tech person, I want to be able to know how certain components interacts with lets say a database, when it comes to the point I have to revisit.
In words I would describe them as this
Main page
-> sign up page
->sign up connects to database if successful go to thank you page.
->sign up connects to database if successful go back to sign up page.
-> contact us
-> etc...
To describe a user interfaces (a web site), I prefer state machines. Each state of the state machine matches a state of you user interface, and the system reacts to the user interaction by changing its state. In each state you state what happens when the system is in that state by adding actions to the state. The actions show how the interface interacts with the system.