1) copy the tabber.js and tabs.css to ...\Scripts. Yes there might be a more appropriate spot for the .css file but since it is a companion to tabber.js it made since to have to live together.
2) Modify your themes Head.cshtml file to load the tabber.js script and tabs.css style sheet. I'm using the default theme so: ...\Themes\DefaultClean\Views\Shared\Head.cshtml
Html.AddScriptParts("~/Scripts/tabber.js");
Html.AppendCssFileParts(string.Format("~/Scripts/tabs.css", themeName));
3) Wrap up your text in the tabber tags as shown in the docs and copy the markup, go to your product details page and use tools-><>Source code button to bring up the source code window and paste your markup in there.
I saw there was a plug-in to add tabs which I suspect is easier and I might eventually move to but for now this is 'free' and lets me move over my existing layout more easily.