Story points are an arbitrary measure of how difficult each phase of a story will be to implement. They are used by scrum teams to represent the effort and complexity of a project, rather than the hours that actually go into completing tasks and objectives—a model that's useful when team size, productivity, and other external factors can't be predicted.
Because every team works at a different rate, you might not be able to predict the exact time frame of any given story—but representing the effort as story points can provide a constructive framework for future planning and implementation. All of this depends, though, on accurately predicting story points.
As a rule, the most effective story point calculation comes from the collaboration of your entire team. As you discuss story points, start with a list of tasks that can be divided into stories. Select the simplest of these tasks and set the story points for this task at 2. The points value of other tasks will be calculated relative to this value.
From there, you'll tackle the other stories individually, allowing each team member to vote on a story points value, then discussing the votes in order to understand why certain tasks are more or less complex than others. For a truly effective story points model, you’ll need to take each team member's input under consideration and reach a consensus on each task before moving on to the next. Through this process, you'll create a system that makes it easier to estimate the time frame for a variety of tasks and to assign fair, motivating targets for your team.