A three-minute video tutorial that describes how to set up MathJax with a Tumblr blog is now available under Demos: Use in Web Platforms. While some of the specifics in this video apply only to Tumblr, the approach is very general and this tutorial will help to set up MathJax in many other online environments as well.
It is very easy to use MathJax with web platforms, thanks to the MathJax CDN service. The key step is to add a link to the CDN service in the HTML header of your web documents. In Tumblr, as well as in most many other blogging environments, this can be done by inserting a little code snippet into the HTML template. With this link in place, you are ready to include LaTeX or MathML in your posts. MathJax will then read these expressions and show beautifully rendered equations to your readers.
The video tutorial offers step-by-step instructions that show you how to open up the HTML header in Tumblr and how to include a link to the MathJax CDN. Please take a look at the Tumblr tutorial and let us know what other tutorial topics you would like to see.