Generally, the person cannot enter the country doing the sanctioning. It would be illegal for, in this case Russian, companies or organizations to do business with these individuals. If they have any financial or other assets within Russian financial systems or otherwise in the country, these may be seized or just frozen. Russian financial systems in general would be restricted from working with them. Even if Russian based companies are operating in other countries, these companies may also be restricted from doing business with these individuals. There may be other specific stipulations, but this is generally what is meant when a specific individual is sanctioned by a nation.