By default, tasks, schedule entries and notes are filed on day pages. This makes it easy for you to see all the entries relevant to a single day without becoming overwhelmed with information. Unfinished tasks are carried over to the next day when you use M-x plan, so it's always kept up to date. Completed tasks are left on the day page you finished them on, which helps when reviewing one's progress and writing accomplishment reports.
You can associate your tasks with projects either when you create the task or later, with M-x planner-replan-task. This makes it easy for you to see all the information associated with a particular project. If you use RememberMode to create notes, you will also be able to associate notes with a plan page.
If your tasks don't usually have dates, you can turn day pages off by
customizing planner-use-day-pages. If so, then all of your
tasks and notes will be stored on the WelcomePage and/or a plan page.