There are not really many steps:
Here you have a simple explanation:
https://letsencrypt.org/howitworks/
Alternatively here are the big docs: https://letsencrypt.readthedocs.org/en/latest/index.html
But as far as I understand these are mainly for contributors of the LE client.
Edit: Sorry, just note that you mentioned IIS. Currently there is no support for IIS in the official LE client, but you can manually get a cert and use a guide for IIS to let it work there.
Related: ASP.Net websites