How to deal damage where the player is looking?

You'd need to find a unit vector to control range. To do that you'd calculate the magnitude of the vector, (find the differences between the player and their target's x/y/z positions, square them, add them together, and then take the square root.) If you divide the x/y/z components by the magnitude, you'll get a 'unit vector,' which has the same direction, but a length of exactly 1, meaning you can multiply it to control the range. (You could also just check if the magnitude exceeds a certain number.) TBH, I imagine you'll have more trouble targeting an entity, I'm pretty sure look angles are mostly just used for getting blocks.