The Shower was added as part of The Bathroom Update (See also Toilet, Basin and Bin).
It is a two-block-high structure, like the Fridge, which you can walk into.
When placed below a Shower Head, right clicking on the top half of the Shower will cause the Shower to turn on. Right clicking again will turn it off. The textures used are Quartz for the floor and edges, and Glass Pane for the walls.