what are the mechanism of submarine?

Answer 1

Most conventional submarines are electrically powered whilst submerged. When running at "periscope depth", they use a snokel for air inlet and exhaust - running their diesel engines to charge the batteries, and for propulsion.

Nuclear engines use closed loop steam turbines to power the craft using the heat of the nuclear pile to create steam.

Answer 2

Let's start at the stern and work forward. Rudder, Screws (props), prop shafts, propulsion unit, helm, periscope, torpedo tubes, missile tubes, radar, sonar.