The blog post about Mash Maker says that the extension enables mashups to become part of your normal browsing experience – the aim being that mashups can be used by anyone, not just techies. The Mash Maker toolbar displays buttons representing appropriate mashups (from a shared community database) that the service thinks you might want to apply to your current page. Clicking on one of these buttons then applies that mashup to your page.
From the product overview page:
Intel Mash Maker is an extension to your existing web browser that allows you to easily augment the page that you are currently browsing with information from other websites. As you browse the web, the Mash Maker toolbar suggests Mashups that it can apply to the current page in order to make it more useful for you. For example: plot all items on a map, or display the leg room for all flights.
Intel Mash Maker learns from the wisdom of the community. Any user can teach Mash Maker new mashups, using a simple copy and paste interface, and once one user has taught Mash Maker a mashup, this mashup will be automatically suggested to other users. Intel Mash Maker also relies on the community to teach it about the structure and semantics of web pages, using a built in structure editor.
Edit: Some videos with usage examples are available here.