system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what the diffrence between a Battleship, Cruiser, Destroyer, Frigate, ect?

Is there an actual difference or is it all just about size of the ships or amount of fire power?
gpt
A Battleship is an obsolete type of ship that exists in no current navy.  They have thick armour and large guns.  

A Cruiser is a ship that is designed to be able to run independently of a fleet, even though they were quite often found in fleets.  They were considered the poor country's Battleships.  They had thick armour and big guns, but not to the same standard of a Battleship.

Destroyers and Frigates are pretty similar and what one nation calls one another will call the other.  They were generally small ships that were for things such as escorting larger ships (they would be the picket line of defence) and also for submarine hunting.

You also had Battlecruisers which were more lightly armoured Battleships.  They could hit as hard as a Battleship but couldn't take as much damage in return.

Aircraft Carriers kind of describe themselves.

Submarines operate under the water.  WW2 subs usually operated on the surface and only submerged when the enemy was spotted.  Today nuclear powered submarines can spend months under water.  

Minesweepers would detect and detonate mines.  They used a variety of methods to do this.  One would be to have large nets that would snag mines as the ship went along.