If you don't know the 'Souls' games, then the 'Dark Souls III' opening cinematic will likely be puzzling at best. Of course, if you do know the 'Souls' game, then you ought to be more comfortable knowing that this cinematic contains some important story fragments that will only be put together and understood after carefully searching the game's nooks and crannies for corroborating text and other narrative snippets.
Indeed, it's quite simple and common the beat a 'Souls' game without grasping the things described in the opening.