I know, this might be a stupid question, but I only know about see-battles from pirate-movies (like Pirates of the Carribean) or such games (AC: Black Flag). But how did naval battles look like, before the ships were equipped with cannons? Did they still try to sink the enemy ships, but with ballistas and catapults? Or did they try to board the enemy ship and kill the other soldiers? Thanks for your help!
I'm all ears for new insights, but in the meantime, this question has been asked a bunch of times, so you can start with the link from the FAQ:
How would a naval battle have taken place before cannons? (by /u/EyeStache)
or checking out these previous threads that came up in a search for "naval warfare before cannons".
The main purpose built warships from antiquity until the adoption of canon was the Galley.
Galleys are shallow draft, single mast, oared rams. These ships were fast, maneuverable and independent of wind. But extremely expensive.
Medieval commanders would often commandeer merchant Cogs and built simple battlements. Cog combat was archers and ballistas and boarding actions by men-at-arms. The Battle of Sluys (1340) is an excellent example of this combat.
The battle of Sluys was the first battle of the Hundred Years' War, Edward III of England claimed the crown of France. Edward's fleet of 160 ships were mainly Cogs. He's deployed 2 ships of archers with one ship of men-at-arms.
The French fleet of 200 ships were Cogs, galleys, and barges. The French chained their ships together and blocked the estuary to the harbor. The English waited until the wind and sun was right then attacked in the afternoon. The combat was violent but the French defensive strategy stopped them from being able to maneuver. The English bowmen raked the decks while English men-at-arms stormed the ships.
The French lost 20,000 dead and 190 captured ships compared to trivial English loss.
Source: Medieval Maritime Warfare: Charles d Stanton
Source: Battles of the medieval world