@gigipuspca - start with the newbies thread in my signature. cIOS are used to start games. This guide puts all the cIOS's that you'll likely ever need on your wii for you. You (or your loader) chooses one when u launch a usb game. Having them available as spec'ed in this guide will give you everything you need.
Make your wii crash? Um, well, with any softmod there is a possibility for error. But the risks are largely mitigated in this guide. I wouldn't worry about it.