Once you have selected your trigger you are presented with an empty workflow canvas to which you can add more steps. To add a step, drag from the connectors panel on the left onto the main canvas. Dropping anywhere will add the new step at the end of the workflow, or you can drop the connector onto an empty branch node or the small plus (+) icon to place it at a specific point in the workflow.
Each step in the workflow corresponds to a call to a 3rd party service or built-in function. When building the workflow, the main edit graph shows the flow of execution when the workflow runs, i.e. the order in which steps are executed.
Use the connector panel search box to filter for a specific connector you are looking for.