The Department of State has released the names of individuals added to the Department of Treasury's List of Specially Designated Nationals and Blocked Persons (SDN List), due to their involvement in harmful activities related to the Russian government. This action was taken under an Executive Order, and as a result, any property these individuals have in the U.S. is now blocked. Additionally, U.S. citizens are not allowed to conduct any transactions with them. More information about the sanctions can be found on the Office of Foreign Asset Control (OFAC) website.
Simple Explanation
The U.S. government found some people working with Russia who are doing bad things, and now these people can't use their stuff in the U.S., and no one in the U.S. is allowed to do business with them.