Hi Shaun,
Most cameras have ahousing like the one below that has corresponding buttons so you can access all the cameras controls through the housing. there are a few cameras that dont need a housing but are really designed for using around water like surfing etc rather than diving as they have a depth limit of 10m while a normal housing mat give you a depth of 30-40m. Hope this helps.
Cameras Underwater: Fuji WP-FXF30 underwater housing and Ikelite 6154.20, 6154.30 for F20 and F30, F31fd