Create neurons
Press the 
button or press "N". Neurons will be created at a default location, at the last location you've clicked on the screen, or to the right of the last created neuron (hence pressing or "N" repeatedly will create a line of neurons). Then double click on one or a group of neurons to set their properties (e.g. what type of neuron they are). For more click here.
Connect neurons
Select one or more source neurons then either (1) right-click or control-left click on the target neuron and choose "connect" in the pop-up menu or (2) left-click on a target neuron while holding down the option and control keys. Then click on one or a group of weights to set their properties. For more click here.
Select screen-items
Left-click to lasso. Shift-left-click or lasso unselects or reselects what is already selected. Keyboard "N" selects all nodes, "W" selects all weights, "A" selects all. For more click here.
Copy /paste
Control-c copies selected items and control-v pastes them at the last point clicked on screen. Copying and repeatedly right-click and pasting at desired locations can be used to create many duplicates of the same network pattern. For more click here.
Increase / decrease values of nodes or weights.
Use the arrow keys on selected objects. Or open the neuron or weight preference dialogs and manually change activation (neurons) or strength (weights). For more click here.
Change properties of nodes or weights.
Select the neurons or weights you want to change and double-click on of the selected items. You can also use right-click and the popup menu or the network menu. If you select both weights and neurons, which preference dialog comes up depends on which kind of item you click on.