Series[f, {x, $x_0$, n}]x=$x_0$ up to order n. For elementary expressions, Series returns the explicit power series as a SeriesData expression:
series = Series[Exp[x^2], {x,0,2}]
The expression created is a SeriesData object:
series // FullForm
Replacing x with does a value produces another SeriesData object:
series /. x->4
Normal transforms a SeriesData expression into a polynomial:
series // Normal
(series // Normal) /. x-> 4
Clear[series];
We can also expand over multiple variables:
Series[Exp[x-y], {x, 0, 2}, {y, 0, 2}]
See also SeriesCoefficient and SeriesData.