Click your left mouse button when the point of the pencil is located at the upstream end of the channel. The channel will appear as a stretching line as you move the cursor. Clicking again will fix the downstream end of the channel, which must be attached to a node, detention basin or other object.

You can enter several channel reaches without having to refer back to the Toolbar or Draw menu by holding down the shift key as you click. If you enter a channel by mistake, place your mouse pointer on the line and press the right mouse button to open a pop-up menu. Select Delete to remove the channel.  Alternatively, left-click on the line to make "handles" appear and press the "delete" key on your keyboard.

To enter data for this channel you need to right-click while holding the mouse pointer onto a point along the channel. This opens a pop-up menu.  Selecting Edit Data from this opens the Irregular Open Channel property sheet.