Are you self-employed and just want to enter your miles driven, to count as an expenses for your self-employment work?
If that's the case, open your return and search for mileage and you'll get an answer with blue buttons. Select the Self-Employed Mileage button and follow the screens. If you haven't already, you'll be asked to answer a few questions about your self-employment work first.
If you need other help regarding entering miles driven, return here and post a comment.