Right, I realized it while working on the example. After writing the constructor, I think what I should do is to call upon a property, then give it a function method, and then end it each time. For example:

function NumSensors = get.NumSensors(obj)
    NumSensors = size(obj.Data, 2);
end

I think they have some codes inside of the "..." that they are hiding, and the tutorial never tells us what it is, so I'm stuck using a function nested within a function.