WordPress is the 600-pound gorilla of the blogosphere. You can start for free at wordpress.com, under a name like yourname.wordpress.com, but if your resource usage exceeds some limit, you have to switch to one of their paid plans.
Or if you'd rather DIY, you can get your own domain name and buy a web-hosting plan with a single-click WordPress installation procedure from any of a bunch of web-hosting providers. For example, I use Namecheap.com for my domain registrar and web hosting. A .net or .com domain name costs about $11 per year with them, and their entry-level web-hosting plan is about $10 for the first year and $39 for succeeding years. If your blog becomes wildly successful, you'll probably have to upgrade to a more expensive hosting plan, but the entry-level one should work fine for starters. I don't use WordPress (I write all my web page code by hand), but my hosting account's control panel has a button for installing it.
You can use MathJax, the equation processor that PF uses, with WordPress. You need to call a MathJax script on your pages, either by editing your WordPress theme or by installing a plugin. Google for "mathjax and wordpress" for details.