no it is not an extension or a plugin within photoshop. imageready used to be a separately installed application in previous versions, but now it comes bundled with photoshop and can be installed at the same time during photoshop installation. it does have close integration with photoshop because you can switch to imageready through photoshop while working on a document.
yes there is an export feature which i think is for outputing to a scanner or PDF, but in his case since he want to make an animated GIF he should use the "save optimized as" option or "save optimized". "export original" would also not work in his case. the save optimized option in imageready is equivalent to photoshop's "save for web" option.
you also have to remember to save the photoshop file with the animation you created otherwise the layer, animation, image maps, and slices are lost because GIF does not save these features within the file.