When opening the program, only the gas source is present in the scheme. Now you need to place all the other objects on the scheme.
Click the button on the left with the desired type of object (consumer/splitter/reductor/pump). After that, left-click on the places where you want to place objects of this type.
Select one or more nodes. After that, click the middle button (mouse wheel) on the node to which you want to connect the selected ones.
If there is no wheel in the mouse (for example, it is not a mouse, but a laptop touchpad), right-click on the second node and select "Lay pipe here" from the context menu.
Click the "Parameters" button on the left for set the gas parameters (density, viscosity).
The window of parameters of objects and pipes is called by double-clicking on them.