Ethical decision-making is the study of how to determine which actions we ought to perform, given the information available to us about the world and about what we should value. Ethical decision-making can be divided into idealized ethical decision-making and practical ethical decision-making.
Idealized ethical decision-making is analogous to standard decision theory, but applied to ethical problems. For any set of actions, values, and beliefs about the world, idealized ethical decision theory will produce an ethical ranking of those actions: it will advise which act is best, given the evidence and what is valued.
But it can be difficult to apply idealized ethical decision-making in practice. This is because the number of actions available at any given time is vast, and the possible effects of actions are difficult to foresee. Practical ethical decision-making includes some direct approximations of idealized ethical decision-making, as well as conceptual handles or approximations which make it easier to act upon limited knowledge of a small part of the world.