The Department of State has announced that several individuals have been added to the Department of Treasury's List of Specially Designated Nationals and Blocked Persons (SDN List). This is because they have been found to be involved in harmful activities related to the government of the Russian Federation, as outlined in an Executive Order. These individuals now have all their property and interests under U.S. jurisdiction blocked, and U.S. persons are generally not allowed to engage in transactions with them. The list and more details about the sanctions can be found on the OFAC website.
Simple Explanation
The U.S. government has decided to block the money and things that some people have in America because they did bad things with Russia. People in the U.S. can't do business with these people now.