What do I need to start making Let's Plays & walkthroughs on YouTube?

I want to start creating/making Let's Plays (LPs) and/or walkthroughs of video games and upload them onto YouTube. I would want my LPs to have my voice, and I wouldn't have commentary on walkthroughs. What equipment do I need to purchase whether at the store like a Best Buy or online? Is there free downloads of the stuff I need or do I need to pay for those downloads as well? What do I need to provide my voice for the commentary? I don't know, it seems complicated, and the stuff I'm asking about I might be leaving some important questions out accidentally. So can someone help and answer these questions? Thanks.