In your code you have a Symbol s that is not declared before the line Begin line. Because of this it is created in that specified Afak10`Private` context. (Also, your code presently has an error; it needs to be Begin["Private`"].) You can include the Global` context if that is in fact the Symbol you wish to return:
f[x_] := Module[{}, x^2 + Global`s]; (* as part of your package *) Now using the function:
f[z] s + z^2
Nevertheless I caution you about this method as you generally should not use (plain) global Symbols like this; instead use Formal Symbols which are Protected to prevent accidental assignment.
f[x_] := Module[{}, x^2 + \[FormalS]]; It looks like this:
