How can I copyright things I write?

They're already copyrighted once they're written down. You can add a copyright symbol on your site and a message to remind people that this is your work that you own the rights to and that they'll need your written permission to use it. Or, you can give them a right to reprint it if they link to the original work on your site.

But, if you're too afraid of people stealing your work or using it without your permission then you shouldn't put it over the web. Also, no offense to you, but most stuff posted over the Internet isn't worth stealing.

I used to have a website where I gave funny advice and everything I wrote on that site was automatically copyrighted by me. The only thing I did was add a copyright symbol at the bottom of each page, but I didn't mind if people quoted from it, copy/pasted on another site, or linked to it - as long as I was given credit or they linked back to my site. But, it wasn't something I was going to sue over if someone claimed it as theirs. I might sent them a nice email asking them to give me credit or remove it, but it's not something worth suing over unless they're making money off it - a lot of money -> This is just my opinion. Oh, and, BTW, people did copy/paste on forums stuff from my site, but they did also link to the original site. I was quite proud. I also have a bunch of journals and I put some of them on the Internet and I was surprised to see people quoting passages from my personal journal. I think that made me the proudest, lol. (You can do a simple search to find out these things.)

Your work is copyrighted from the moment you save it to a fixed medium, like paper or your hard drive. Adding the copyright symbol offers no additional protection. Registering the copyright (which costs $45) protects you only if you can prove a theft for profit and can subpoena the person to appear in a US court--good luck if they live somewhere else.

If you post good work on a website, you cannot really protect it from being stolen. If that's your worry, there's only one solution: don't post it at a public website.

Just put the little copyright symbol at the start of your work, and people will see, because everything anyone writes is automatically copyrighted as soon as it's written.

copyright happens as soon as you write something. You can write-protect your website, but there is nothing you can do to stop people from stealing. Not even God has manged that