NumberForm[expr, n] prints with approximate real numbers in expr given to n-digit precision.
NumberForm[expr, n, f] prints with approximate real numbers having n digits, with f digits to the right of the decimal point.
NumberForm works on integers as well as approximate real numbers.
The following options can be given:
All options except ExponentFunction apply to integers as well as approximate real numbers.
You can mix NumberForm and BaseForm.
NumberForm acts as a "wrapper", which affects printing, but not evaluation.
See The Mathematica Book: Section 2.8.7.
See also: ScientificForm, EngineeringForm, AccountingForm, BaseForm, PaddedForm, N.