sorry, I don't specifically know how to add comments for the webs.com platform - just pick one that looks good and follow directions on the site
I'm no expert and I taught myself for the most part, so I'm sure you can do it too
if the sites are free, you might want to start a demo/test site to try different things on - might save you some heartache if something breaks
javascripts are just lines of code that do something for your site - you just cut and paste them into the right places in your HTML and you are good to go, ...usually
another option might be to embed a blog into a page on your site, but I don't specifically know how to do that either
anyway, have fun with it, that should be your first goal
take care and good luck