How do I insert clip art in Pages document?

Copy and Paste, or go Insert (menu) > Choose..., locate and select the image file, and click Insert.

Images pasted into a placeholder frame will automatically resize to fit the frame.

Explore, using some of the templates that include pictures.

Regards,

Barry

In addition to Barry's comments, you can also drag and drop clipart into your Pages document. This can be most common formats including PDF, Photoshop (.psd), Illustrator (.ai), .png, .jpg, .eps (will be converted to PDF), .tiff, .icns (icon format), and gif. The .svg format is not supported at this time.