Mmh. I think there is a kind of confusion here.
A bidet is a kind of porcelain device with the approximate shape of a toilet where one can wash the genitals, the bottom or the feet. They are named like this because early models, were meant to be straddled, as a horse would be, to wash the genitals or bottom, and bidet is an old name for a kind of horse in French.
A bidet :
https://en.zity.biz/gallery/image/264063
This young woman is washing her pubes on a bidet :
https://en.zity.biz/gallery/image/273387
Another picture on using a bidet:
https://en.zity.biz/gallery/image/277409
Bidets have largely fallen out of fashion in France but are to be found in almost all Italian bathrooms in homes or hotel rooms, where they are typically set next to the toilet:
https://en.zity.biz/gallery/image/273463
This is a 18th century model:
https://en.wikipedia.org/wiki/Bidet#/media/File:Boilly_La_Toilette_intime_ou_la_Rose_effeuill%C3%A9e.jpg
A foldable model, see the shape for straddling:
https://commons.wikimedia.org/wiki/File:Bidet_portatil_a%C3%B1o_1910.jpg
Bidets used to be used especially by menstruating women. In addition they seem to have been used for washing or douching post coitum.
A bidet seat is a special toilet seat meant to provide the functions of washing the anus and vulva that one could perform on a bidet. The Japanese are found of these; you may press on a button (with a pictogram of buttocks) to wash the bottom, and another button (with a pictogram of a woman and some water flowing up) to wash the vulva.
A picture of the controls on a Japanese bidet toilet seat:
https://en.zity.biz/gallery/image/273103