In parametric mode, the calculator will plot a parameter curve: for every number t, it calculates a point with coordinates x(t),y(t).
Of course, the calculator cannot calculate ALL points because there are infinitely many numbers.
Rather, it will start at Tmin, and in every step add Tstep, until it arrives at Tmax.
For instance, if Tmin = -2, Tmax = 4 and Tstep = 0.1, it will calculate the points belonging to
... t = -2.0, t = -1.9, t = -1.8, ... , t = 3.9, t = 4.0.