Your question is ambiguous: do you just want some way of entering the definite integral in Wolfram|Alpha? Or, instead, do you want the Mathematica (i.e., Wolfram Language) form,
If the latter, then Otto Linsuain gave the answer.
But if the former, then among other possibilities, the following works:
integrate x for x from -2 to 3
So does the shorter form:
integrate x from -2 to 3
