When you drive a car, you typically don't drive the same speed the whole time. The car's speedometer changes as you drive and tells you the instantaneous speed at that moment in time. 

The current through a wire functions in a similar way: current changes at different points in time because the flow of electrons through the wire is changing. This means that the number of charges passing through one part of the wire is changing. Imagine pausing time and then measuring the current in the wire at one point--that is the instantaneous current.

This NetLogo model does not measure the exact instantaneous current. So, to estimate instantaneous current, the model takes a very small amount of time which simulates one instant. This small amount of time is called the sampling rate and can be adjusted in the model using the "sampling-rate" slider. Remember that NetLogo time units are called ticks.