if you want to add your site on stumble upon. sign up on stumble upon and then go to profile ...here is a option (left hand side) add my page ...by click on this add you website .
Let me update this thread , Since Stumble has updated to stumble upon beta , so now way of adding blog , website, pics , photos to stumble has changed , read more to add your website or blog in stumble to get awesome traffic to your web or blog http://shoutingblogger.blogspot.com/2012/10/how-to-add-page-to-stumbleupon.html (this is not my blog just a follower) https://www.youtube.com/watch?v=XkFQVTbGcz4 [video=youtube;XkFQVTbGcz4]https://www.youtube.com/watch?v=XkFQVTbGcz4[/video]
If you have a big site with around 50 pages I would recommend you get someone to do it for you as it is way time consuming. It is very cheap you can find it out fiverr for example. I found one and I actually used it. The link is: http://fiverr.com/familyhols/put-up-to-50-urls-on-stumbleupon-for-more-traffic . Sorry but I don't mean to spam or anything just you may find it helpful
You can easily add your site in stumble upon in your profile section. You can add the link in the profile section. To add a page you need to click on the add page option. You need to browse others website to get visitors or visits for your own website.