Your Starting Class Doesn’t Matter
As with all the previous Souls games, your starting class in Dark Souls III doesn’t affect a lot outside of what equipment and stats you start with. If you picked the Warrior starting class and decide that you want to become a sorcerer later on, you can always allocate points to your Intelligence stat and start casting powerful spells. Dark Souls III also allows you to respec your character with the use of certain items, so you don’t have to worry about getting locked into one specific play style.
That said, there are a few classes that are a bit more beginner-friendly, and this is important especially for newer players. For beginners, I recommend starting out with either the Knight or Warrior class. The Warrior has higher HP to start with, and the high damage boost will aid you greatly in the first few boss fights of the game. Similarly, the Knight also has good damage output, and he has one attunement slot just in case you want to make use of pyromancy in your run. Alternatively, the Herald could also be a good choice if you want a well-rounded starting class capable of wielding most types of weapons.
We would recommend going with the classic sword-and-shield build for newcomers. To that end, the Knight and Warrior class will serve you especially well in the first few hours of the game.