hosting provider/server administrator can do it for you.
SSL is a piece of code on your server that encrypts the information being sent to and from the server so that to someone viewing the data over the wires it looks like random bits. They don't know what any of it means.
Usually your server admin will create a folder (e.g. named 'secure') on your server that you want to serve encrypted documents from. You then place the files to be encrypted in that folder and point the relevant URL to it, for example secure.dailypaul.com or dailypaul.com/secure/somepage.html. You can also encrypt the entire site which is what I recommend. See the Bitcoin exchange https://mtgox.com for example.
The certificate is less important. It's a long story, but you can self-sign your own certificate to save money (won't look good to browsers though). Using one from a "trustted authority" like Thawte is good for appearances, but that system is broken (again, long story).
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