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Here's a general concept for each class. Our game has a wealth of depth to it, so there's a lot of information that goes much deeper than this.
Carriers - Resource-based Decision-class. Do you help the left flank? The right flank? Do you go for damage or for team influence? Do you push your hull forward or hide?
Battleships - Tough Threat-class. You can take positions and be hard to dislodge due to armor. Your guns are very threatening because of their size, but your accuracy is low to prevent you from one-shotting everything~
Cruiser - Utility Middle-ground class. You have more consistent damage output, consumable options (hydro/radar), mediocre armor, decent speed, medium health... You can provide assistance in many situations, but you are not as sneaky as a Destroyer and not as tanky as a Battleship.
Destroyer - Frontline Stealth-class. Destroyers have very low detection (excepting some gun-boat lines). They can use this advantage to scout and use torpedoes from stealth. This class is expected to play forward and aggressively... but have little health and armor so not -too aggressive-~
Submarine - Frontline Ambush-class. Submarines are able to be extremely stealthy for short durations of time. They can use this to take unexpected positions or ambush unsuspecting enemies. These are new so there are not many learning resources available (youtube video series/coaches).
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Sidenote: German Carriers are an advanced CV line. I would recommend starting out with the US Line first, and then considering either the IJN or Russian CV line after.
Each Nation/Shiptype has its own type of identity. A new player likely won't notice much difference between one Cruiser and another Cruiser, but experienced players learn their nuances in play.
You started German which tends to have better armored ships (Battleships/Cruisers/Carriers), torpedoes on most ships, excellent Hydrophone consumables, comfortable firing ballistics, strong AP damage, and weak but consistent HE damage (among other things).