The Wireframes category contains special types of web parts that are not intended for designing actual website pages. Instead, they serve as wireframing components that you can use to create schematics directly in the content tree of a website. This can be done in the CMS Desk -> Content interface on the Wireframe tab of dedicated wireframe documents or other document types that contain a wireframe definition.
To learn more about wireframes in general, please see the Development -> Wireframing chapter of the Developer's Guide.
This section of the web part reference provides information about the wireframe components that are included in the default Kentico CMS installation.