In Taverna 2.x, you can add a new input by right-clicking on the white space in the Workflow Diagram and selecting Insert -> Workflow input port, or by selecting the red triangle icon from the toolbar at the top of the Workbench.
In Taverna 1.7.x, you can add a new input by right-clicking on the Workflow inputs node in the Advanced Model Explorer tree, and select Create new input… option.
