Creating a aimbot

Just a wondering I wan't to create my own aimbot , but I don't want a regular aimbot such as one that just points everywhere and gets you banned. From my understanding I learned all you need is health, team pos , x y z coords of your self and enemy xyz , but I don't understand the formula for example something like this
float
GetMagnitude(Vector3D vec)
{
return sqrt(pow(vec.x, 2) + pow(vec.y, 2) + pow(vec.z, 2)); not sure which formula this is , but i understand it to degree
}

Vector3D SubtractVec(Vector3D src, Vector3D dest) same here
{
Vector3D vec(0, 0, 0); I was wondering if someone can come give me better understanding of this concept
vec.x = dest.x - src.x;
vec.y = dest.y - src.y;
vec.z = dest.z - src.z;

return vec;
}

Im trying to create a fov aimbot and since this is C++ im doing it in im guessing all math is already built in can someone give me a full sourcecode of a full aimbot that is or has worked I want to understand everything so i can really understand it yes I know c++ I looked plenty videos on youtube but I never get the full view of everything or a place where it tells me everything i need for a aimbot?