How to add audio to replay

Hey guys. Im new to editing videos and so forth, but I want to get started. Were doing a series with some lesser experienced people, and I wantmto help them with positioning , line, etc., so i want to make videos where I can show a replay of a lap or track with a real time explanation of key points, corners, etc, kind of how johnny oconnell does before SCCA World Challenge races. So what is the easiest way to lay simple voice recorded audio or add it to a Forza 4 replay?

Record your voice with Audacity and adding it with the video using video editing software is the simplest way possible.