Sprint Planning Meetings are held at the beginning of an iteration to plan the work that will be undertaken by the Team. The Scrum Master, Product Owner and the Team, along with any stakeholders who hold an interest in any of the products being considered will be in attendance.
The Product Owner by this point will have groomed the Product Backlog, by this I mean he / she will have reordered the Product Backlog Items into a priority order. Depending on the size of the backlog, the Product Owner may choose to only present the highest priority items to the team or depending on the Teams velocity, the items that fall within that figure. The Product Backlog will then be presented to the team.
The Team will then have the opportunity to ask questions or ask for further information in order for them to gain enough scope so that the Team can go off and discuss what the work will entail. My Team usually have the primary meeting to uncover which tasks will be considered for the Sprint and then take an hour to go discuss or mull over the items in their own time with no pressure to commit to anything right away.
The secondary meeting involves the Team planning which Stories they will move from the Product Backlog to the Sprint Backlog and theoretically committing to the work that they will carry out during the sprint (see image)
The Team will meet with the product owner to discuss what they feel they will be able to commit to during the sprint. It may be that some stories that are of high priority are just to big to fit into the one sprint and may need broken down into smaller, more manageable stories or some stories of a lower priority may have to be completed in order for the higher placed stories to be worked on. This will lead to negotiation with the product owner as to which backlog items will be added to the Sprint Backlog and once the Product Owner is happy with the commited list we can then go onto writing the tasks for each of the stories.
With the Sprint Backlog Items defined the Team will then collectively decide on a Sprint Goal. A short sharp and to the point goal that the team will have reached by the end of the sprint. The team will then aim to have obtained that goal by the end of the sprint.