Entertainers are a type of Utilities building. You can find them in the Services section of the Build Menu. They will boost the overall fun of your park. Like other Utilities, they have a range, and must be placed carefully to ensure maximum coverage of your paths.
You will also notice that each entertainer will get out of its booth to roam around the area they cover. The Peeps will also acknowledge the entertainers and give you their feedback on them!