Vect is a typedef of Point - at least it was in the Betas.
Point(float x, float y) and Vect(float x, float y) is therefor equal.
In turn, this means you can du this:
-9.8f is merely an approximation of earths gravity.
To clearify the syntax:
Vect gravity(0, -9.8f);
Btw, Vect is not std::vector<> if that's what made the confusion
Hope this helps you.