New to Dark Souls, Lothric Knights on the Lothric Wall are kicking my ass

I am a very calm player when it comes to games but this is absurd. I just beat Sekiro with like 0 problems so I decided to try DS3. I just cannot realiably kill the Lothric Knights are are literally in the first 15 minutes of the game. What the hell am I supposed to do? I've read that people say just keep rolling but as soon as I roll he does a chain attack and gets me with the second attack whilst im getting up. I also just cannot get behind them(using a mouse and keyboard). I've watched people on youtube kill them and its almost like their character moves differently when they are circling the mobs, like it hops a little towards the left or right. I don't understand why you would put such a tough enemy so early on the game. I'm playing a knight. The halbeard knight attacks so quickly sometimes that its impossibility to roll. I really wanna enjoy this game and continue playing but I am so close to deleting and refunding it. Can somebody tell me a step by step guide of what I am supposed to do? Rolling just doesn't work, they just attack me before I stand up.