  We present McMule, a unified framework for the calculation of NLO and NNLO
corrections to many processes in QED with massive fermions. This easily
extendable program allows users to calculate an arbitrary observable for any of
the processes implemented. These include various lepton decays as well as
certain low-energy scattering experiments such as $e\mu\to e\mu$ and $\ell
p\to\ell p$ that can be measured to high enough a precision to warrant QED
corrections.
  As part of our discussion, we will present a pedagogical introduction to how
these calculations are performed, focusing on technical aspects supplemented
with examples. Our goal is to provide a useful introduction for those entering
the field, covering all aspects relevant for the practitioner.
