Unless it's changed in the past few years, Moonfruit is a service which provides its own hosted content management system, which includes its own blogging facilities.
As far as I can see, you can embed a WordPress blog within your Moonfruit site, but WordPress isn't actually installed and hosted on Moonfruit as part of your site. So, you could have a blog from WordPress.com, and have it displayed within your site.
This is a very clunky way of doing it, and it's only worth doing if you want to connect an existing Wordpress.com blog to an existing Moonfruit site. TBH Moonfruit is only really worth it for small traders who want an easy, cheap way of having a basic brochure site. It's not really suitable for anything more complex, such as setting up a blog which you hope will grow.
For a new blog-orientated site I'd avoid Moonfruit altogether, and install WordPress on a separate hosting package (such as HostPresto). WordPress gives you far more flexibility and is more geared towards SEO: over time you can really make the blog your own.
If it's more of a 'hobby' blog then Moonfruit might do - but I'd use Moonfruit's blog tools rather than the kludge of embedding WordPress. WordPress is far superior, but embedding it will just confuse visitors and search engines.