Currently they are using a ring vaccination strategy and vaccinating confirmed close contacts of infected people with the JYNNEOS vaccine. This is a modern smallpox vaccine that works against monkeypox as well. It can be used for pre and post exposure prophylaxis, and it can even help after infection.
Over the coming weeks they'll expand it to people with confirmed and presumed monkeypox exposures. The latter group to include men who have sex with men who have recently had multiple sex partners in a venue where there was known to be monkeypox or in an area where monkeypox is spreading. Anyone that has close sustained contact with someone with monkeypox and their lesions can get infected, but many cases so far have been among men who have sex with men who have recently had multiple sex partners.
The US has large stockpiles of the ACAM2000 vaccine as well. However this vaccine has more side effects than JYNNEOS and will be reserved.
Here are some pictures of the monkeypox rash. In some cases lesions are only seen around the genital area. Cases are still extremely low in the US with only 306 cases across 27 states. This is just a proactive measure to contain the outbreak.