Thank You! There are two errors - square brackets in Sum and zero initial value s, after fix it works
x =.
s =.
x = 1 - (2 s)^0.5
\[Alpha] = 0.5
n = 4
A = 1 - x^n - \!\(
\*UnderoverscriptBox[\(\[Sum]\), \(k = 0\), \(\(-1\) + n\)]
\*FractionBox[\(
\*SuperscriptBox[\(x\), \(k\)] \((1 -
\*SuperscriptBox[\(x\), \(\(-k\) + n\)])\)\), \(\(-k\) + n\)]\)
p = 1 - x
b = \[Alpha] A*(1 - x)^2/(A + 1 - x^n)
data = Table[Table[{s, f}, {s, 0.0001, 1, 0.01}], {f, {p, b}}];
ListLinePlot[data, PlotLegends -> {price, ad}]
