Clear[x, y]

x[n_, k_] := N[k/n]

y[n_, 0] := 1

y[n_, k_] := N[(1 - (2/n))^k]

Clear[T]

T[n_, a_] := Table[{x[n, k], y[n, k]}, {k, 0, a*n}]

T[5, 2]

Clear[G]

G[n_, a_] := 
      ListPlot[T[n, a], PlotStyle -> Hue[0.6], 
        AspectRatio -> Automatic, PlotRange -> {0, 1}, 
        PlotJoined -> True]

G[3, 2]

G[4, 2]

G[10, 2]