When you click the Digg link below the headline of a Reuters.com article, your submission will appear in Digg's “Upcoming Stories” area, where other Digg members can find it and, if they like it, Digg it as well.
Once a submission has earned a critical mass of Diggs, it becomes “popular” and jumps to the Digg homepage in its category. If it becomes one of the most popular, it qualifies as a “Top 10”. If a submission doesn't receive enough Diggs within a certain time period, it eventually falls out of the “Upcoming” section.
To find out more about how Digg works, go to the "How Digg Works" page at http://www.digg.com/how.