What is underwater housing for?

The waterproof housing case is essentially a camera case for your Digital camera, but one that allows full control of the camera when diving, is waterproof and pressure-proof, so the case is designed for Sepecfic camera& Lens models, you should check the compatible list before purchasing.
Matched Camera: for Nikon Z7 II, Compatible with Nikon Z6 II (Not Compatible with Frist Generation）

(If your Camera is Nikon Z7/ Z6, Please contact the seller）

Compatible lenses

For NIKON AF-S 16-35 1:4G ED
For NIK SP 24-70 F2.8
AF-S VR105 F/2.8G IF-ED
AF-S 8-15 1:3.5-4.5 ED
Key features:

Interchangeable port system
Vacuum Pump System port
Sync cable port
High-quality optical viewfinder
The inbuilt leak detection sensor
Fiber optic port
Stainless steel mounting plate 1/4" Thread
The reinforced metallic bottom plate
Multi-coated optical glass lens port
Package Including:

1x Underwater housing Body for Z6 II/Z7II
1x Flat standard port
1x User manual
1x Spare O'ring
1x Shoulder strap
1x Wrist strap
1x Lens protective cover
​1x Clean Cloth