To link ports manually, click Layout > Link Columns. When you drag from one port to another, the Designer creates a connection. When you drag a port into an empty port, the Designer copies the port and creates a connection.
You can also link multiple ports at the same time. Use the Ctrl or Shift key to select a range of ports to link to another transformation. The Designer links the ports, beginning with the top pair. It links all ports that meet the validation requirements.