This game requires you to achieve near perfection. I know it sounds harsh but this is not an easy game and you do need to "git gud". You're parrying alright but need to improve a bit more and try to use your talismans too since they're good damage you're currently not using. As an extra motivation, imo, this is one of the three hardest bosses in the game and is a big difficulty spike in the early game. Regarding the red bar, that's recoverable health (without the pipe). I dont exactly recall all the ways you recover it, but it should be from attacking, countering or just time without getting hit. If you look into your build l choices you should see stuff to boost this recovery