A Sprint Plan (or Iteration Plan) is time-boxed plan of a short duration usually 1 to 4 weeks. The sprint plan will be fine grained, identifying user stories intended for implementation during the sprint/iteration.
A Sprint/Iteration Plan is only valid for an Agile/Iterative team as Continuous Flow teams will simply take the top requirement from the Product Backlog and Waterfall Teams have no concept of fine detailed short-term plans. The terms "Sprint" and "Iteration" are interchangeable. Sprints/Iterations work towards achieving Releases and so Sprint/Iteration Plans are closely related to Release Plans.
Sprint plans are created by the development team by taking user stories from a backlog prioritized by the product customer. For this reason, customers are often included in Sprint planning sessions so that they can balance the priorities and explain any details around the requirements that the team may need to effectively plan.
A Project/Product Manager may be involved to facilitate the planning session but is not responsible for planning - planning is a joint team activity that helps the team understand how they will deliver something; it can't be done by an individual in isolation.
The highest priority story is taken from the backlog and fully planned by the team by thinking about what must be done to reach the required level of done for the story. The team will decide if it can be "Done" in the sprint, and if it can, the story is accepted into the sprint and the team move on to the next story in the backlog. If the story can't be "done" in a sprint it will either need doing in a later sprint (so it's placed back on the backlog) or it's just too big and needs breaking up.
During the sprint/iteration the team will usually track progress using workflow metrics such as a burnup. Planning normally occurs as the first activity in the time box, (or just before the timebox starts) and should include all team members. People should always create their own tasks since they know how best to spend their time and the team knows best how to interact and collaboratively work towards their goals. Planning imposed onto the team by someone (including a Project Manager) is only ever an aspiration.
At the end of the sprint/iteration we recommend that teams hold a retrospective to assess their performance and identify any ways to improve how they work. Customer engagement is essential in delivering a quality product that delivers business goals. For this reason, we recommend a customer demo at the end of each iteration/sprint.
If an iteration/sprint doesn’t result in working software that gets feedback from Customers or their representatives, it’s not a real iteration, just a planning timebox.