What's the process by which the line of sight from a scope and the path of a bullet from a rifle is calibrated?

How does one adjust the scope such that line of sight from the scope and the path from the barrel converge at a certain point? I imagine what’s actually adjusted varies from scope and rifle but the principal must be the same.

Furthermore how do snipers in the military deal with this issue of the scope being offset from the path of the bullet? Can their scopes be pre-configured with several different convergence points? Convergence points being the point at which the line of sight from the scope and the bullet path intersect.