At the beginning of the game you do not need to give any orders on this screen since your land transport occurs automatically each turn. The sliders representing land transport are color coded with green bars.  The green (land) transport is included on the screen only so you can see how many units of each commodity you are receiving. 

Once you build or conquer your first port , you will see blue color-coded sliders representing water transport.  Commodities that are moved by water at any portion of their journey to your capital are displayed as blue.

To see what your computer advisor would do with this water transport, click on the human face in the upper left part of the screen.  The icon changes to a computer and the transport screen is set to computer control. You may choose to leave the screen this way, or restore human control and make changes in the orders entered by the computer.

To increase or decrease your water transport manually, click on the gold arrows to either side of a slider that is all blue or has some blue in it.   Alternatively you may click within the slider bar.