Featured within Black Desert is a host of different Boss encounters, ranging from solo to group fight, and a few raid bosses that require the effort of a multitude of players to bring down.
Most bosses are clearly indicated by their immense size and glowing red eyes, along with signature moves where those with keen eyes can read the tells and avoid massive damage.
Most of the bosses you will encounter in game are summoned via scrolls that you collect when farming NPC's. These usually require a decent amount depending on your farm speed and the difficulty of the boss you may need as many as 6 components to complete a scroll.
In many instances you can enlist the help of a group to take down bosses, however in order to do so you must have the group formed prior to summoning. This only applies to bosses that don't naturally spawn in the world, and require the use of an item to summon them.