To connect two Web Flows you have to use the Go To Destination element, where you specify where to redirect the flow. The Select Destination window allows you to indicate the flow and the screen where you want to jump.
The Go To Destination element can also be used to link Web Screens of the same Web Flow. For example, this could be useful when, for a matter of organization, you don't want to connect them directly and graphically.
Select Destination Window | Connect Web Screens | Go To Destination Properties