There are several ways it could be done. You would start by using their Widget Builder to generate the html for it, then you could either put it in the layout.master file of your skin so it would be on every page of your site, or you could put just the javascript in the layout.master and put the html part into a content template which you would then insert into the blog posts (or any content) from the editor.

To paste in raw html you have to go to the source view of the editor which shows the raw html. There is a button in the editor toolbar to get to the source view.

oh, and the javasacript must go in the layout.master file of your skin which is located under /Data/Sites/[SiteID]/skins/[skinname]

skinname is shown in the skin dropdown in site settings, siteid is usually 1 unless its a multi site installation

putting in in the one in App_MasterPages isn't going to work