You can see where one passage leads to the next by the flow lines that connect the passages. Hover your mouse over a passage to see which passages lead into it (in blue) and where the conversation can flow after it (in orange). Passages can also lead to passages in other conversations.
You can click-and-drag passages to arrange them in your flow. Passage flow lines automatically adjust to the passage's position. Moving a passage on the canvas is considered a change, and will appear in draft stage in Versions.